Practice Test - Laws of motion, Work, Power & Energy Class 9 Notes | EduRev

Class 9 : Practice Test - Laws of motion, Work, Power & Energy Class 9 Notes | EduRev

 Page 1


                                   [1] 
 
 
 
Test -03  (Laws of motion, Work, Power & Energy) 
 
1. An object of mass 10 kg. moves at a constant 
speed of 10 ms
-1
. A constant force, that acts for 4 
sec on the object. Gives it is speed of 2 ms
-1
 in 
opposite direction. The force acting on the object 
is :   
(a) -3N (b) -30 N   
(c) 3 N (d) 30 N 
2. A block of mass M is pulled along horizontal 
frictionless surface by a rope of mass m. Force P is 
applied at one end of rope. The force which the 
rope exerts on the block is :   
(a) 
m M
P
+
 (b) 
) M m ( M
P
+
  
(c) 
) M m (
PM
+
 (d) 
m M
P
-
 
3. A uniform rope of length L resting on a 
frictionless horizontal surface is pulled at one end 
by a force F. What is the tension in the rope at a 
distance ? from the end where the force is 
applied :  
(a) F   (b) ) L / 1 ( F ? +  
(c) F/2  (d) ) L / 1 ( F ? - 
4. A machine gun has a mass 5 kg. It fires 50 gram 
bullets at the rate of 30 bullets per minute at a 
speed of 400 ms
-1
. What force is required to keep 
the gun in position :  
(a) 10 N  (b) 5 N   
(c) 15 N (d) 30 N 
5. A man weighing 80 kg is standing on a trolley 
weighing 320 kg. The trolley is resting on 
frictionless horizontal rails. If the man starts 
walking on the trolley along the rails at a speed of 
one metre per second, then after 4 seconds, his 
displacement relative to the ground will be :   
(a) 5 metres  (b) 4.8 metres   
(c) 3.2 metres  (d) 3.0 metres 
6. The elevator shown in fig. is descending with an 
acceleration of 2 m/s
2
. The 
mass of the block A = 0.50 
kg. the force exerted by the 
block A on block B  is :   
(a) 2 N   
(b) 4 N   
(c) 6 N   
(d) 8 N  
7. A particle of mass 10 kg is 
moving in a straight line if its displacement x with 
time t is given by           x = (t
3
 - 2t - 10)m, then the 
force acting on it at the end of 4 seconds is :  
(a) 24 N  (b) 240 N  
(c) 300 N  (d) 1200 N  
8. When force F
1
, F
2
, F
3
 are acting on  a particle of 
mass m such that F
2
 and F
3
 are mutually 
perpendicular. Then the particle remains 
stationary. If the force F
1
 is now removed then the 
acceleration of the particle is :  
(a) 
m
F
1
 (b)  
1
3 2
mF
F F
 
(c) 
m
F F
3 2
-
 (d) 
m
F
2
 
9.   A body moves with uniform velocity on a rough 
surface, under the action of a force. The force F of 
dynamic friction is plotted against time as shown 
below. The graph will be :  
  
10. A particle moves in a circle of radius 25 cm at two 
revolutions per seconds. The acceleration of the 
particle in metre per second is :  
(a) p
2
 (b)  8 p
2
 
(c) 4 p
2
 (d) 2 p
2
 
11. An automobile of mass m is crossing over a 
convex upwards over bridge with a speed v. If the 
radius of the bridge is r, The thrust on the bridge 
at the highest point will be :  
(a) mg + 
r
mv
2
 (b)  
r
mv
mg
2
- 
(c) 
r
g v m
2 2
 (d) 
r
g v
2
 
12. The ratio of angular speeds of minute’s hand and 
hour’s hand of a watch is  : 
(a) 1 : 12  (b) 6 : 1  
(c) 12 : 1  (d) 1 : 6  
13. A particle is moving along a circular path with a 
uniform speed. Through what angle does its 
angular velocity change when it completes half of 
the circular path :  
(a) 0 ° (b) 45 ° 
(c) 180 ° (d) 360 ° 
14. Three identical blocks of masses m = 2 kg are 
drawn by a force F = 10.2 N on a frictionless 
surface, then what is the tension (in N) in the 
string between the blocks B and C ? 
Page 2


                                   [1] 
 
 
 
Test -03  (Laws of motion, Work, Power & Energy) 
 
1. An object of mass 10 kg. moves at a constant 
speed of 10 ms
-1
. A constant force, that acts for 4 
sec on the object. Gives it is speed of 2 ms
-1
 in 
opposite direction. The force acting on the object 
is :   
(a) -3N (b) -30 N   
(c) 3 N (d) 30 N 
2. A block of mass M is pulled along horizontal 
frictionless surface by a rope of mass m. Force P is 
applied at one end of rope. The force which the 
rope exerts on the block is :   
(a) 
m M
P
+
 (b) 
) M m ( M
P
+
  
(c) 
) M m (
PM
+
 (d) 
m M
P
-
 
3. A uniform rope of length L resting on a 
frictionless horizontal surface is pulled at one end 
by a force F. What is the tension in the rope at a 
distance ? from the end where the force is 
applied :  
(a) F   (b) ) L / 1 ( F ? +  
(c) F/2  (d) ) L / 1 ( F ? - 
4. A machine gun has a mass 5 kg. It fires 50 gram 
bullets at the rate of 30 bullets per minute at a 
speed of 400 ms
-1
. What force is required to keep 
the gun in position :  
(a) 10 N  (b) 5 N   
(c) 15 N (d) 30 N 
5. A man weighing 80 kg is standing on a trolley 
weighing 320 kg. The trolley is resting on 
frictionless horizontal rails. If the man starts 
walking on the trolley along the rails at a speed of 
one metre per second, then after 4 seconds, his 
displacement relative to the ground will be :   
(a) 5 metres  (b) 4.8 metres   
(c) 3.2 metres  (d) 3.0 metres 
6. The elevator shown in fig. is descending with an 
acceleration of 2 m/s
2
. The 
mass of the block A = 0.50 
kg. the force exerted by the 
block A on block B  is :   
(a) 2 N   
(b) 4 N   
(c) 6 N   
(d) 8 N  
7. A particle of mass 10 kg is 
moving in a straight line if its displacement x with 
time t is given by           x = (t
3
 - 2t - 10)m, then the 
force acting on it at the end of 4 seconds is :  
(a) 24 N  (b) 240 N  
(c) 300 N  (d) 1200 N  
8. When force F
1
, F
2
, F
3
 are acting on  a particle of 
mass m such that F
2
 and F
3
 are mutually 
perpendicular. Then the particle remains 
stationary. If the force F
1
 is now removed then the 
acceleration of the particle is :  
(a) 
m
F
1
 (b)  
1
3 2
mF
F F
 
(c) 
m
F F
3 2
-
 (d) 
m
F
2
 
9.   A body moves with uniform velocity on a rough 
surface, under the action of a force. The force F of 
dynamic friction is plotted against time as shown 
below. The graph will be :  
  
10. A particle moves in a circle of radius 25 cm at two 
revolutions per seconds. The acceleration of the 
particle in metre per second is :  
(a) p
2
 (b)  8 p
2
 
(c) 4 p
2
 (d) 2 p
2
 
11. An automobile of mass m is crossing over a 
convex upwards over bridge with a speed v. If the 
radius of the bridge is r, The thrust on the bridge 
at the highest point will be :  
(a) mg + 
r
mv
2
 (b)  
r
mv
mg
2
- 
(c) 
r
g v m
2 2
 (d) 
r
g v
2
 
12. The ratio of angular speeds of minute’s hand and 
hour’s hand of a watch is  : 
(a) 1 : 12  (b) 6 : 1  
(c) 12 : 1  (d) 1 : 6  
13. A particle is moving along a circular path with a 
uniform speed. Through what angle does its 
angular velocity change when it completes half of 
the circular path :  
(a) 0 ° (b) 45 ° 
(c) 180 ° (d) 360 ° 
14. Three identical blocks of masses m = 2 kg are 
drawn by a force F = 10.2 N on a frictionless 
surface, then what is the tension (in N) in the 
string between the blocks B and C ? 
                                   [2] 
 
 
 
 
(a) 9.2 (b) 8 
(c) 3.4 (d) 9.8 
15. Work is always done on a body when :  
(a) a force acts on it   
(b) it moves through a certain distance   
(c) it experience an increase in energy through a 
mechanical influence   
(d) none of the above  
16. A weight hangs freely from the end of a spring. A 
body then slowly pushes the weight upwards 
until the spring becomes slack. The gain in 
gravitational potential energy of the weight 
during this process is equal to :  
(a) the workdone by the boy against the gravity 
force acting on the weight   
(b) the loss of stored energy by the spring minus 
the work done by the tension in the spring   
(c) the workdone on the weight by the boy plus 
the stored energy lost by the spring   
(d) the workdone on the weight by the boy 
minus the workdone by the tension in the 
spring plus the stored energy lost by the 
spring  
17. A light and a heavy body have equal momentum. 
Which one has greater K.E. :  
(a) The light body   
(b) Both have equal K.E.   
(c) The heavy body   
(d) Data given is incomplete  
18. A shell initially at rest explodes into two equal 
fragments A and B. Then :  
(a) A and B have collinear velocities in the same 
direction   
(b) A and B have equal speeds but opposite 
velocities   
(c) A and B have equal speeds but their 
velocities inclined to each other    
(d) A and B may have unequal speeds but 
opposite velocities  
19. One end of a light spring of spring constant k is 
fixed to a wall and the other end is tied to a block 
placed on a smooth horizontal surface. In a 
displacement, the work done by the spring is 
2
1
k 
x
2
. The possible cases are :   
(a) The spring was initially compressed by a 
distance x, was finally in  its natural length  
(b) It was initially stretched by a distance x and 
was finally in its natural length   
(c) It was initially in its natural length and 
finally in a compressed position   
(d) Both (a) & (b) are correct 
20. Choose the correct statement.  Work done by a 
variable force : 
(a) it defined as  S . F
? ?
  
(b) Is independent of path  
(c) Is always dependent on the initial and final 
positions   
(d) None of these 
21. Work done by friction :  
(a) Is always negative   
(b) Is always zero   
(c) May be negative zero or positive   
(d) Is always positive  
22. The example (s) of conservative force is/are :  
(a) Gravitational force   
(b) Spring force   
(c) Electrostatic force   
(d) All the above  
23. A particle describes a horizontal circle of radius 
0.5 m with uniform speed. The centripetal force 
acting is 10 N. The work done in describing a 
semicircle is :  
(a) zero  (b) 5 J   
(c) 5 pJ (d) 10 pJ 
24. A boy pushes a toy box 2.0 m along the floor by 
means of a force of 10 N directed downward at an 
angle of 60 ° to the horizontal. The work done by 
the boy is :  
(a) 6 J  (b) 8 J  
(c) 10 J (d) 12 J 
25. Two masses m 1
 = 5 kg and m
2
 = 4.8 kg tied to a 
string are hanging over a light frictionless pulley. 
What is the acceleration of the masses what left 
free to move ? (g = 9.8 m/s
2
)  
 
(a) 0.2 m/s
2
 (b) 9.8 m/s
2
 
(c) 5 m/s
2 
(d) 4.8 m/s
2
 
In every question a statement of ASSERTION is 
followed by a statement of REASON. Mark the 
correct answer out of the following choices:  
If both ASSERTION and REASON are true and reason 
is the correct explanation of the assertion. 
(a) If both ASSERTION and REASON are true 
but reason is not the correct explanation of the 
assertion. 
(b) If ASSERTION is true but REASON is false. 
(c) If ASSERTION is false but REASON is true. 
Page 3


                                   [1] 
 
 
 
Test -03  (Laws of motion, Work, Power & Energy) 
 
1. An object of mass 10 kg. moves at a constant 
speed of 10 ms
-1
. A constant force, that acts for 4 
sec on the object. Gives it is speed of 2 ms
-1
 in 
opposite direction. The force acting on the object 
is :   
(a) -3N (b) -30 N   
(c) 3 N (d) 30 N 
2. A block of mass M is pulled along horizontal 
frictionless surface by a rope of mass m. Force P is 
applied at one end of rope. The force which the 
rope exerts on the block is :   
(a) 
m M
P
+
 (b) 
) M m ( M
P
+
  
(c) 
) M m (
PM
+
 (d) 
m M
P
-
 
3. A uniform rope of length L resting on a 
frictionless horizontal surface is pulled at one end 
by a force F. What is the tension in the rope at a 
distance ? from the end where the force is 
applied :  
(a) F   (b) ) L / 1 ( F ? +  
(c) F/2  (d) ) L / 1 ( F ? - 
4. A machine gun has a mass 5 kg. It fires 50 gram 
bullets at the rate of 30 bullets per minute at a 
speed of 400 ms
-1
. What force is required to keep 
the gun in position :  
(a) 10 N  (b) 5 N   
(c) 15 N (d) 30 N 
5. A man weighing 80 kg is standing on a trolley 
weighing 320 kg. The trolley is resting on 
frictionless horizontal rails. If the man starts 
walking on the trolley along the rails at a speed of 
one metre per second, then after 4 seconds, his 
displacement relative to the ground will be :   
(a) 5 metres  (b) 4.8 metres   
(c) 3.2 metres  (d) 3.0 metres 
6. The elevator shown in fig. is descending with an 
acceleration of 2 m/s
2
. The 
mass of the block A = 0.50 
kg. the force exerted by the 
block A on block B  is :   
(a) 2 N   
(b) 4 N   
(c) 6 N   
(d) 8 N  
7. A particle of mass 10 kg is 
moving in a straight line if its displacement x with 
time t is given by           x = (t
3
 - 2t - 10)m, then the 
force acting on it at the end of 4 seconds is :  
(a) 24 N  (b) 240 N  
(c) 300 N  (d) 1200 N  
8. When force F
1
, F
2
, F
3
 are acting on  a particle of 
mass m such that F
2
 and F
3
 are mutually 
perpendicular. Then the particle remains 
stationary. If the force F
1
 is now removed then the 
acceleration of the particle is :  
(a) 
m
F
1
 (b)  
1
3 2
mF
F F
 
(c) 
m
F F
3 2
-
 (d) 
m
F
2
 
9.   A body moves with uniform velocity on a rough 
surface, under the action of a force. The force F of 
dynamic friction is plotted against time as shown 
below. The graph will be :  
  
10. A particle moves in a circle of radius 25 cm at two 
revolutions per seconds. The acceleration of the 
particle in metre per second is :  
(a) p
2
 (b)  8 p
2
 
(c) 4 p
2
 (d) 2 p
2
 
11. An automobile of mass m is crossing over a 
convex upwards over bridge with a speed v. If the 
radius of the bridge is r, The thrust on the bridge 
at the highest point will be :  
(a) mg + 
r
mv
2
 (b)  
r
mv
mg
2
- 
(c) 
r
g v m
2 2
 (d) 
r
g v
2
 
12. The ratio of angular speeds of minute’s hand and 
hour’s hand of a watch is  : 
(a) 1 : 12  (b) 6 : 1  
(c) 12 : 1  (d) 1 : 6  
13. A particle is moving along a circular path with a 
uniform speed. Through what angle does its 
angular velocity change when it completes half of 
the circular path :  
(a) 0 ° (b) 45 ° 
(c) 180 ° (d) 360 ° 
14. Three identical blocks of masses m = 2 kg are 
drawn by a force F = 10.2 N on a frictionless 
surface, then what is the tension (in N) in the 
string between the blocks B and C ? 
                                   [2] 
 
 
 
 
(a) 9.2 (b) 8 
(c) 3.4 (d) 9.8 
15. Work is always done on a body when :  
(a) a force acts on it   
(b) it moves through a certain distance   
(c) it experience an increase in energy through a 
mechanical influence   
(d) none of the above  
16. A weight hangs freely from the end of a spring. A 
body then slowly pushes the weight upwards 
until the spring becomes slack. The gain in 
gravitational potential energy of the weight 
during this process is equal to :  
(a) the workdone by the boy against the gravity 
force acting on the weight   
(b) the loss of stored energy by the spring minus 
the work done by the tension in the spring   
(c) the workdone on the weight by the boy plus 
the stored energy lost by the spring   
(d) the workdone on the weight by the boy 
minus the workdone by the tension in the 
spring plus the stored energy lost by the 
spring  
17. A light and a heavy body have equal momentum. 
Which one has greater K.E. :  
(a) The light body   
(b) Both have equal K.E.   
(c) The heavy body   
(d) Data given is incomplete  
18. A shell initially at rest explodes into two equal 
fragments A and B. Then :  
(a) A and B have collinear velocities in the same 
direction   
(b) A and B have equal speeds but opposite 
velocities   
(c) A and B have equal speeds but their 
velocities inclined to each other    
(d) A and B may have unequal speeds but 
opposite velocities  
19. One end of a light spring of spring constant k is 
fixed to a wall and the other end is tied to a block 
placed on a smooth horizontal surface. In a 
displacement, the work done by the spring is 
2
1
k 
x
2
. The possible cases are :   
(a) The spring was initially compressed by a 
distance x, was finally in  its natural length  
(b) It was initially stretched by a distance x and 
was finally in its natural length   
(c) It was initially in its natural length and 
finally in a compressed position   
(d) Both (a) & (b) are correct 
20. Choose the correct statement.  Work done by a 
variable force : 
(a) it defined as  S . F
? ?
  
(b) Is independent of path  
(c) Is always dependent on the initial and final 
positions   
(d) None of these 
21. Work done by friction :  
(a) Is always negative   
(b) Is always zero   
(c) May be negative zero or positive   
(d) Is always positive  
22. The example (s) of conservative force is/are :  
(a) Gravitational force   
(b) Spring force   
(c) Electrostatic force   
(d) All the above  
23. A particle describes a horizontal circle of radius 
0.5 m with uniform speed. The centripetal force 
acting is 10 N. The work done in describing a 
semicircle is :  
(a) zero  (b) 5 J   
(c) 5 pJ (d) 10 pJ 
24. A boy pushes a toy box 2.0 m along the floor by 
means of a force of 10 N directed downward at an 
angle of 60 ° to the horizontal. The work done by 
the boy is :  
(a) 6 J  (b) 8 J  
(c) 10 J (d) 12 J 
25. Two masses m 1
 = 5 kg and m
2
 = 4.8 kg tied to a 
string are hanging over a light frictionless pulley. 
What is the acceleration of the masses what left 
free to move ? (g = 9.8 m/s
2
)  
 
(a) 0.2 m/s
2
 (b) 9.8 m/s
2
 
(c) 5 m/s
2 
(d) 4.8 m/s
2
 
In every question a statement of ASSERTION is 
followed by a statement of REASON. Mark the 
correct answer out of the following choices:  
If both ASSERTION and REASON are true and reason 
is the correct explanation of the assertion. 
(a) If both ASSERTION and REASON are true 
but reason is not the correct explanation of the 
assertion. 
(b) If ASSERTION is true but REASON is false. 
(c) If ASSERTION is false but REASON is true. 
                                   [3] 
 
 
 
26. Assertion : When a car crashes head on into a 
heavy truck, the car experiences a 
greater change in momentum. 
 Reason     :  Newton’s second law states that the 
change in momentum is equal to 
impulse. 
27. Assertion : When a force acts on a body, it can 
change its momentum and kinetic 
energy  
 Reason     :  A force produces acceleration  
28. Assertion : No work is done when a man is 
whirling a stone tied to a rope in a 
circle with a constant speed. 
 Reason     : The centripetal force is 
perpendicular to the direction of 
displacement.   
29. Assertion : Kilowatt hour (Kwh) is the unit of 
electric power.   
 Reason     : Watt hour has units of energy.  
30. Assertion : A body builder does no work in 
holding up a weight.  
 Reason     : No work is done because the 
displacement moved is zero. 
 
 
   
 
 
 
 
 
Test -02 (Set - B) Medical     C10    (Laws of motion, Work, Power & Energy)   ANSWER KEY 
 
1 
B 
6 
B 
11 
B 
16 
C 
21 
C 
26 D 
2 
C 
7 
B 
12 
C 
17 
A 
22 
D 
27 A 
3 
D 
8 
A 
13 
A 
18 
B 
23 
A 
28 A 
4 
A 
9 
B 
14 
C 
19 
D 
24 
C 
29 D 
5 
C 
10 
C 
15 
C 
20 
C 
25 A 30 A 
 
SOLUTIONS 
1. Here, u = 10 ms
-
1
, v = - 2ms
-
1
 ;   t = 4 s, a = ? 
Using a = 
2
s / m 3
4
10 2
t
u v
- =
- -
=
-
, Force, F = ma 
= 10 × ( -3) = - 30 N  
2. Acceleration of block, a = 
mass total
force
= 
m M
P
+
 ?  
Force on block = mass × acceleration = Ma = 
m M
MP
+
. 
3. Let m be the mass per unit length of rope. 
Therefore, mass of rope = mL. Acceleration in the 
rope due to force F will be a = F/mL mass of rope 
of length (L - ) ? will be m (L - ) ? . Therefore, 
tension in the rope of length (L - ) ? , is equal to 
pulling fore on it = m(L - ) ? a = m(L - ) ? × F/mL = 
F(1 - ) L / ? 
4. Force required = 
taken time
momentum in change
= 
N 10
60
400 ) 30 10 50 (
3
=
× × ×
-
 
5. (c) Due to conservation of momentum 80 × 1 = (80 
+ 320)V ? V = 
5
1
 = 0.2 m/s. Velocity of man wrt 
ground =- 1 – 0.2 = 0.8 m/s. ?Displacement of 
man ground = (0.8 m/s) × 4s = 3.2 m 
6. F = mg - R = 0.5 × 10 - 0.5 × 2 = 5 - 1 = 4N  
7. m = 10 kg, x = (t
3
 - 2t - 10)m  ?   2 t 3 v
dt
dx
2
- = = 
and t 6 a
dt
x d
2
2
= = At the end of 4 secs, a = 6 × 4 = 24 
m/s
2
  
F = ma = 10 × 24 = 240 N. 
8. The formula for force is given by F
1
 = ma. 
Acceleration of the particle a = 
m
F
1
  
9. Dynamic friction force is constant 
10. (c) a = rw
2
 = 
4
1
× (2 p ×2)
2
 = 
4
1
× 4 p
2
  = 4 p
2
 
11. Mg – N = 
r
mv
2
 ? N = mg - 
r
mv
2
. 
12. Angular speed of hour hand.  ?
1
 = 
) 60 12 (
2
×
p
. 
Angular speed of minute hand ?
2
 = 
60
2 p
 ?  
1
12
60
60 12
1
2
=
×
=
?
?
 
Page 4


                                   [1] 
 
 
 
Test -03  (Laws of motion, Work, Power & Energy) 
 
1. An object of mass 10 kg. moves at a constant 
speed of 10 ms
-1
. A constant force, that acts for 4 
sec on the object. Gives it is speed of 2 ms
-1
 in 
opposite direction. The force acting on the object 
is :   
(a) -3N (b) -30 N   
(c) 3 N (d) 30 N 
2. A block of mass M is pulled along horizontal 
frictionless surface by a rope of mass m. Force P is 
applied at one end of rope. The force which the 
rope exerts on the block is :   
(a) 
m M
P
+
 (b) 
) M m ( M
P
+
  
(c) 
) M m (
PM
+
 (d) 
m M
P
-
 
3. A uniform rope of length L resting on a 
frictionless horizontal surface is pulled at one end 
by a force F. What is the tension in the rope at a 
distance ? from the end where the force is 
applied :  
(a) F   (b) ) L / 1 ( F ? +  
(c) F/2  (d) ) L / 1 ( F ? - 
4. A machine gun has a mass 5 kg. It fires 50 gram 
bullets at the rate of 30 bullets per minute at a 
speed of 400 ms
-1
. What force is required to keep 
the gun in position :  
(a) 10 N  (b) 5 N   
(c) 15 N (d) 30 N 
5. A man weighing 80 kg is standing on a trolley 
weighing 320 kg. The trolley is resting on 
frictionless horizontal rails. If the man starts 
walking on the trolley along the rails at a speed of 
one metre per second, then after 4 seconds, his 
displacement relative to the ground will be :   
(a) 5 metres  (b) 4.8 metres   
(c) 3.2 metres  (d) 3.0 metres 
6. The elevator shown in fig. is descending with an 
acceleration of 2 m/s
2
. The 
mass of the block A = 0.50 
kg. the force exerted by the 
block A on block B  is :   
(a) 2 N   
(b) 4 N   
(c) 6 N   
(d) 8 N  
7. A particle of mass 10 kg is 
moving in a straight line if its displacement x with 
time t is given by           x = (t
3
 - 2t - 10)m, then the 
force acting on it at the end of 4 seconds is :  
(a) 24 N  (b) 240 N  
(c) 300 N  (d) 1200 N  
8. When force F
1
, F
2
, F
3
 are acting on  a particle of 
mass m such that F
2
 and F
3
 are mutually 
perpendicular. Then the particle remains 
stationary. If the force F
1
 is now removed then the 
acceleration of the particle is :  
(a) 
m
F
1
 (b)  
1
3 2
mF
F F
 
(c) 
m
F F
3 2
-
 (d) 
m
F
2
 
9.   A body moves with uniform velocity on a rough 
surface, under the action of a force. The force F of 
dynamic friction is plotted against time as shown 
below. The graph will be :  
  
10. A particle moves in a circle of radius 25 cm at two 
revolutions per seconds. The acceleration of the 
particle in metre per second is :  
(a) p
2
 (b)  8 p
2
 
(c) 4 p
2
 (d) 2 p
2
 
11. An automobile of mass m is crossing over a 
convex upwards over bridge with a speed v. If the 
radius of the bridge is r, The thrust on the bridge 
at the highest point will be :  
(a) mg + 
r
mv
2
 (b)  
r
mv
mg
2
- 
(c) 
r
g v m
2 2
 (d) 
r
g v
2
 
12. The ratio of angular speeds of minute’s hand and 
hour’s hand of a watch is  : 
(a) 1 : 12  (b) 6 : 1  
(c) 12 : 1  (d) 1 : 6  
13. A particle is moving along a circular path with a 
uniform speed. Through what angle does its 
angular velocity change when it completes half of 
the circular path :  
(a) 0 ° (b) 45 ° 
(c) 180 ° (d) 360 ° 
14. Three identical blocks of masses m = 2 kg are 
drawn by a force F = 10.2 N on a frictionless 
surface, then what is the tension (in N) in the 
string between the blocks B and C ? 
                                   [2] 
 
 
 
 
(a) 9.2 (b) 8 
(c) 3.4 (d) 9.8 
15. Work is always done on a body when :  
(a) a force acts on it   
(b) it moves through a certain distance   
(c) it experience an increase in energy through a 
mechanical influence   
(d) none of the above  
16. A weight hangs freely from the end of a spring. A 
body then slowly pushes the weight upwards 
until the spring becomes slack. The gain in 
gravitational potential energy of the weight 
during this process is equal to :  
(a) the workdone by the boy against the gravity 
force acting on the weight   
(b) the loss of stored energy by the spring minus 
the work done by the tension in the spring   
(c) the workdone on the weight by the boy plus 
the stored energy lost by the spring   
(d) the workdone on the weight by the boy 
minus the workdone by the tension in the 
spring plus the stored energy lost by the 
spring  
17. A light and a heavy body have equal momentum. 
Which one has greater K.E. :  
(a) The light body   
(b) Both have equal K.E.   
(c) The heavy body   
(d) Data given is incomplete  
18. A shell initially at rest explodes into two equal 
fragments A and B. Then :  
(a) A and B have collinear velocities in the same 
direction   
(b) A and B have equal speeds but opposite 
velocities   
(c) A and B have equal speeds but their 
velocities inclined to each other    
(d) A and B may have unequal speeds but 
opposite velocities  
19. One end of a light spring of spring constant k is 
fixed to a wall and the other end is tied to a block 
placed on a smooth horizontal surface. In a 
displacement, the work done by the spring is 
2
1
k 
x
2
. The possible cases are :   
(a) The spring was initially compressed by a 
distance x, was finally in  its natural length  
(b) It was initially stretched by a distance x and 
was finally in its natural length   
(c) It was initially in its natural length and 
finally in a compressed position   
(d) Both (a) & (b) are correct 
20. Choose the correct statement.  Work done by a 
variable force : 
(a) it defined as  S . F
? ?
  
(b) Is independent of path  
(c) Is always dependent on the initial and final 
positions   
(d) None of these 
21. Work done by friction :  
(a) Is always negative   
(b) Is always zero   
(c) May be negative zero or positive   
(d) Is always positive  
22. The example (s) of conservative force is/are :  
(a) Gravitational force   
(b) Spring force   
(c) Electrostatic force   
(d) All the above  
23. A particle describes a horizontal circle of radius 
0.5 m with uniform speed. The centripetal force 
acting is 10 N. The work done in describing a 
semicircle is :  
(a) zero  (b) 5 J   
(c) 5 pJ (d) 10 pJ 
24. A boy pushes a toy box 2.0 m along the floor by 
means of a force of 10 N directed downward at an 
angle of 60 ° to the horizontal. The work done by 
the boy is :  
(a) 6 J  (b) 8 J  
(c) 10 J (d) 12 J 
25. Two masses m 1
 = 5 kg and m
2
 = 4.8 kg tied to a 
string are hanging over a light frictionless pulley. 
What is the acceleration of the masses what left 
free to move ? (g = 9.8 m/s
2
)  
 
(a) 0.2 m/s
2
 (b) 9.8 m/s
2
 
(c) 5 m/s
2 
(d) 4.8 m/s
2
 
In every question a statement of ASSERTION is 
followed by a statement of REASON. Mark the 
correct answer out of the following choices:  
If both ASSERTION and REASON are true and reason 
is the correct explanation of the assertion. 
(a) If both ASSERTION and REASON are true 
but reason is not the correct explanation of the 
assertion. 
(b) If ASSERTION is true but REASON is false. 
(c) If ASSERTION is false but REASON is true. 
                                   [3] 
 
 
 
26. Assertion : When a car crashes head on into a 
heavy truck, the car experiences a 
greater change in momentum. 
 Reason     :  Newton’s second law states that the 
change in momentum is equal to 
impulse. 
27. Assertion : When a force acts on a body, it can 
change its momentum and kinetic 
energy  
 Reason     :  A force produces acceleration  
28. Assertion : No work is done when a man is 
whirling a stone tied to a rope in a 
circle with a constant speed. 
 Reason     : The centripetal force is 
perpendicular to the direction of 
displacement.   
29. Assertion : Kilowatt hour (Kwh) is the unit of 
electric power.   
 Reason     : Watt hour has units of energy.  
30. Assertion : A body builder does no work in 
holding up a weight.  
 Reason     : No work is done because the 
displacement moved is zero. 
 
 
   
 
 
 
 
 
Test -02 (Set - B) Medical     C10    (Laws of motion, Work, Power & Energy)   ANSWER KEY 
 
1 
B 
6 
B 
11 
B 
16 
C 
21 
C 
26 D 
2 
C 
7 
B 
12 
C 
17 
A 
22 
D 
27 A 
3 
D 
8 
A 
13 
A 
18 
B 
23 
A 
28 A 
4 
A 
9 
B 
14 
C 
19 
D 
24 
C 
29 D 
5 
C 
10 
C 
15 
C 
20 
C 
25 A 30 A 
 
SOLUTIONS 
1. Here, u = 10 ms
-
1
, v = - 2ms
-
1
 ;   t = 4 s, a = ? 
Using a = 
2
s / m 3
4
10 2
t
u v
- =
- -
=
-
, Force, F = ma 
= 10 × ( -3) = - 30 N  
2. Acceleration of block, a = 
mass total
force
= 
m M
P
+
 ?  
Force on block = mass × acceleration = Ma = 
m M
MP
+
. 
3. Let m be the mass per unit length of rope. 
Therefore, mass of rope = mL. Acceleration in the 
rope due to force F will be a = F/mL mass of rope 
of length (L - ) ? will be m (L - ) ? . Therefore, 
tension in the rope of length (L - ) ? , is equal to 
pulling fore on it = m(L - ) ? a = m(L - ) ? × F/mL = 
F(1 - ) L / ? 
4. Force required = 
taken time
momentum in change
= 
N 10
60
400 ) 30 10 50 (
3
=
× × ×
-
 
5. (c) Due to conservation of momentum 80 × 1 = (80 
+ 320)V ? V = 
5
1
 = 0.2 m/s. Velocity of man wrt 
ground =- 1 – 0.2 = 0.8 m/s. ?Displacement of 
man ground = (0.8 m/s) × 4s = 3.2 m 
6. F = mg - R = 0.5 × 10 - 0.5 × 2 = 5 - 1 = 4N  
7. m = 10 kg, x = (t
3
 - 2t - 10)m  ?   2 t 3 v
dt
dx
2
- = = 
and t 6 a
dt
x d
2
2
= = At the end of 4 secs, a = 6 × 4 = 24 
m/s
2
  
F = ma = 10 × 24 = 240 N. 
8. The formula for force is given by F
1
 = ma. 
Acceleration of the particle a = 
m
F
1
  
9. Dynamic friction force is constant 
10. (c) a = rw
2
 = 
4
1
× (2 p ×2)
2
 = 
4
1
× 4 p
2
  = 4 p
2
 
11. Mg – N = 
r
mv
2
 ? N = mg - 
r
mv
2
. 
12. Angular speed of hour hand.  ?
1
 = 
) 60 12 (
2
×
p
. 
Angular speed of minute hand ?
2
 = 
60
2 p
 ?  
1
12
60
60 12
1
2
=
×
=
?
?
 
                                   [4] 
 
 
 
13. There is no change in the angular velocity, when 
speed is constant.  
14. a = 
2 3
2 . 10
×
ms
-
1
=
6
2 . 10
 = 1.7 ms
-
2   
; 
 
T = 2 × 1.7N = 
3.4 N 
15. (C)  
16. (C) 
17. (A) 
18. Apply law of conservation of momentum.  
19. Stored elastic potential energy of spring = 
2
1
kx
2
 
where , x is compression or elongation of spring 
from its natural length. In this position the spring 
can do work on the block tied to it, which is equal 
to 
2
1
 kx
2
, so both option (a) and (b) are correct. 
20. The work done by a variable force is defined as W 
= ds . F
?
?
. It may or may not depend on the path 
followed. It is always dependent on the initial and 
final positions. 
21. The work done by friction may be positive, 
negative or zero. Imaging a situation in which a 
block of mass M is pulled horizontally by a force F 
on a rough horizontal surface with coefficient of 
friction µ. If F < µ Mg, then work done by friction 
force is zero. If F > µ Mg, then work done by 
friction force is positive. 
22. All the mentioned forces are the examples of 
conservation force. 
23. W = F s cos 90 ° = zero 
24. W = F s cos ? = 10 × 2 cos 60 ° = 10 J 
25. a=
2 1
2 1
m m
m m
+
-
g = 
8 . 4 5
8 . 4 5
+
-
× 9.8ms
-
2
 = 0.2 ms
-
2
 
26. (d) Assertion is false and reason is true.  
Since the car has smaller mass than the truck, 
the magnitude of its acceleration will be more 
than that of the truck. According to Newton’s 
third law, both the vehicle experience the 
same magnitude of force and the same 
impulse. Therefore, the change in momentum 
for the car and the truck is same. 
27. (a) Both assertion and reason are true and reason 
is the correct explanation. 
When a force produces acceleration, it changes 
the velocity of the body and hence there is 
change in kinetic energy and momentum.  
28. (a) Both assertion and reason are true and reason 
is the correct explanation of the assertion.  
 ? = 
?
F .
?
d = Fd cos90 = 0 ? here 
?
F is 
 towards centre of circle & 
?
d is perpendicular 
 to 
?
F .  
29. (d) Assertion is false and reason is true.  
 Kilowatt (1000 watt) is the unit of power. 
Kilowatt hour is the power consumed in one 
hour = power × time = energy. One watt is 
equal to Joule per second. Hence watt × time 
has units of energy.  
30. (d) Both assertion and reason are true and reason 
is the correct explanation of the assertion.  
W = 
? ?
d . F =Fd cos ? = 0 because d = 0.  
 
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