Work, Energy and Power Practice Questions - DPP for JEE

 Page 1


PART-I (Single Correct MCQs)
1. A spring of spring constant 5 × 10
3
 N/m is stretched initially by 5cm
from the unstretched position. Then the work  required to stretch it
further by another 5 cm is
(a) 12.50  Nm
(b) 18.75  Nm
(c) 25.00  Nm
(d) 6.25    Nm
2. A particle of mass 10 g moves along a circle of radius 6.4 cm with a
constant tangential acceleration. What is the magnitude of this
acceleration if the kinetic energy of the particle becomes equal to 8 ×
10
–4
 J by the end of the second revolution after the beginning of the
motion ?
(a) 0.1 m/s
2
 (b) 0.15 m/s
2
(c) 0.18 m/s
2
(d) 0.2 m/s
2
3. A body is moved  along a straight line by a machine delivering a
constant power.  The distance moved by the body in time ‘t’ is
Page 2


PART-I (Single Correct MCQs)
1. A spring of spring constant 5 × 10
3
 N/m is stretched initially by 5cm
from the unstretched position. Then the work  required to stretch it
further by another 5 cm is
(a) 12.50  Nm
(b) 18.75  Nm
(c) 25.00  Nm
(d) 6.25    Nm
2. A particle of mass 10 g moves along a circle of radius 6.4 cm with a
constant tangential acceleration. What is the magnitude of this
acceleration if the kinetic energy of the particle becomes equal to 8 ×
10
–4
 J by the end of the second revolution after the beginning of the
motion ?
(a) 0.1 m/s
2
 (b) 0.15 m/s
2
(c) 0.18 m/s
2
(d) 0.2 m/s
2
3. A body is moved  along a straight line by a machine delivering a
constant power.  The distance moved by the body in time ‘t’ is
proportional to
(a) t
3/4
(b) t
3/2
(c) t
1/4
(d) t
1/2
4. A ball is thrown vertically downwards from a height of 20 m with an
initial velocity v
0
. It collides with the ground and loses 50% of its
energy in collision and rebounds to the same height. The initial velocity
v
0
 is :    (Take g = 10 ms
–2
)
(a) 20 ms
–1
(b) 28 ms
–1
(c) 10 ms
–1
(d) 14 ms
–1
5. When a rubber-band is stretched by a distance x, it exerts restoring
force of magnitude F = ax + bx
2
 where a and b are constants. The work
done in stretching the unstretched rubber-band by L is:
(a)
(b)
(c)
(d)
6. A particle is acted by a force F = kx, where k is a +ve constant. Its
potential energy at x = 0 is zero. Which curve correctly represents the
variation of potential energy of the block with respect to x
Page 3


PART-I (Single Correct MCQs)
1. A spring of spring constant 5 × 10
3
 N/m is stretched initially by 5cm
from the unstretched position. Then the work  required to stretch it
further by another 5 cm is
(a) 12.50  Nm
(b) 18.75  Nm
(c) 25.00  Nm
(d) 6.25    Nm
2. A particle of mass 10 g moves along a circle of radius 6.4 cm with a
constant tangential acceleration. What is the magnitude of this
acceleration if the kinetic energy of the particle becomes equal to 8 ×
10
–4
 J by the end of the second revolution after the beginning of the
motion ?
(a) 0.1 m/s
2
 (b) 0.15 m/s
2
(c) 0.18 m/s
2
(d) 0.2 m/s
2
3. A body is moved  along a straight line by a machine delivering a
constant power.  The distance moved by the body in time ‘t’ is
proportional to
(a) t
3/4
(b) t
3/2
(c) t
1/4
(d) t
1/2
4. A ball is thrown vertically downwards from a height of 20 m with an
initial velocity v
0
. It collides with the ground and loses 50% of its
energy in collision and rebounds to the same height. The initial velocity
v
0
 is :    (Take g = 10 ms
–2
)
(a) 20 ms
–1
(b) 28 ms
–1
(c) 10 ms
–1
(d) 14 ms
–1
5. When a rubber-band is stretched by a distance x, it exerts restoring
force of magnitude F = ax + bx
2
 where a and b are constants. The work
done in stretching the unstretched rubber-band by L is:
(a)
(b)
(c)
(d)
6. A particle is acted by a force F = kx, where k is a +ve constant. Its
potential energy at x = 0 is zero. Which curve correctly represents the
variation of potential energy of the block with respect to x
(a)
(b)
(c)
(d)
7. A particle of mass m is driven by a machine that delivers a constant
power of k watts. If the particle starts from rest the force on the particle
at time t is
(a)
(b)
(c)
(d)
8. A moving body with a mass m
1
 and velocity u strikes a stationary body
of mass m
2
. The masses m
1
 and m
2
  should be in the ratio m
1
/m
2
 so as to
decrease the velocity of the first body to 2u/3 and giving a velocity of v
Page 4


PART-I (Single Correct MCQs)
1. A spring of spring constant 5 × 10
3
 N/m is stretched initially by 5cm
from the unstretched position. Then the work  required to stretch it
further by another 5 cm is
(a) 12.50  Nm
(b) 18.75  Nm
(c) 25.00  Nm
(d) 6.25    Nm
2. A particle of mass 10 g moves along a circle of radius 6.4 cm with a
constant tangential acceleration. What is the magnitude of this
acceleration if the kinetic energy of the particle becomes equal to 8 ×
10
–4
 J by the end of the second revolution after the beginning of the
motion ?
(a) 0.1 m/s
2
 (b) 0.15 m/s
2
(c) 0.18 m/s
2
(d) 0.2 m/s
2
3. A body is moved  along a straight line by a machine delivering a
constant power.  The distance moved by the body in time ‘t’ is
proportional to
(a) t
3/4
(b) t
3/2
(c) t
1/4
(d) t
1/2
4. A ball is thrown vertically downwards from a height of 20 m with an
initial velocity v
0
. It collides with the ground and loses 50% of its
energy in collision and rebounds to the same height. The initial velocity
v
0
 is :    (Take g = 10 ms
–2
)
(a) 20 ms
–1
(b) 28 ms
–1
(c) 10 ms
–1
(d) 14 ms
–1
5. When a rubber-band is stretched by a distance x, it exerts restoring
force of magnitude F = ax + bx
2
 where a and b are constants. The work
done in stretching the unstretched rubber-band by L is:
(a)
(b)
(c)
(d)
6. A particle is acted by a force F = kx, where k is a +ve constant. Its
potential energy at x = 0 is zero. Which curve correctly represents the
variation of potential energy of the block with respect to x
(a)
(b)
(c)
(d)
7. A particle of mass m is driven by a machine that delivers a constant
power of k watts. If the particle starts from rest the force on the particle
at time t is
(a)
(b)
(c)
(d)
8. A moving body with a mass m
1
 and velocity u strikes a stationary body
of mass m
2
. The masses m
1
 and m
2
  should be in the ratio m
1
/m
2
 so as to
decrease the velocity of the first body to 2u/3 and giving a velocity of v
to m
2
 assuming a perfectly elastic impact. Then the ratio m
1
/m
2
 is
(a) 5
(b)
(c)
(d) 25
9. Two similar springs P and Q have spring constants K
P
 and K
Q
, such that
K
P
 > K
Q
. They are stretched, first by the same amount (case a,) then by
the same force (case b). The work done by the springs W
P
 and W
Q
 are
related as, in case (a) and case (b), respectively
(a) W
P
 = W
Q
 ; W
P
 = W
Q
(b) W
P
 > W
Q
 ; W
Q
 > W
P
(c) W
P
 < W
Q
 ; W
Q
 < W
P
(d) W
P
 = W
Q
 ; W
P
 > W
Q
10. A body is allowed to fall freely under gravity from a height of 10m.  If
it looses 25% of its energy due to impact with the ground, then the
maximum height it rises after one impact is
(a) 2.5m (b) 5.0m (c) 7.5m (d) 8.2m
11. Water falls from a height of 60 m at the rate of 15 kg/s to operate a
turbine. The losses due to frictional force are 10% of energy. How
much power is generated by the turbine?( g = 10 m/s
2
)
(a) 8.1 kW
(b) 10.2 kW
(c) 12.3 kW
(d) 7.0 kW
12. A glass marble dropped from a certain height above the horizontal
surface reaches the surface in time t and then continues to bounce up
and down. The time in which the marble finally comes to rest is
(a) e
n
t
(b) e
2
t
(c)
Page 5


PART-I (Single Correct MCQs)
1. A spring of spring constant 5 × 10
3
 N/m is stretched initially by 5cm
from the unstretched position. Then the work  required to stretch it
further by another 5 cm is
(a) 12.50  Nm
(b) 18.75  Nm
(c) 25.00  Nm
(d) 6.25    Nm
2. A particle of mass 10 g moves along a circle of radius 6.4 cm with a
constant tangential acceleration. What is the magnitude of this
acceleration if the kinetic energy of the particle becomes equal to 8 ×
10
–4
 J by the end of the second revolution after the beginning of the
motion ?
(a) 0.1 m/s
2
 (b) 0.15 m/s
2
(c) 0.18 m/s
2
(d) 0.2 m/s
2
3. A body is moved  along a straight line by a machine delivering a
constant power.  The distance moved by the body in time ‘t’ is
proportional to
(a) t
3/4
(b) t
3/2
(c) t
1/4
(d) t
1/2
4. A ball is thrown vertically downwards from a height of 20 m with an
initial velocity v
0
. It collides with the ground and loses 50% of its
energy in collision and rebounds to the same height. The initial velocity
v
0
 is :    (Take g = 10 ms
–2
)
(a) 20 ms
–1
(b) 28 ms
–1
(c) 10 ms
–1
(d) 14 ms
–1
5. When a rubber-band is stretched by a distance x, it exerts restoring
force of magnitude F = ax + bx
2
 where a and b are constants. The work
done in stretching the unstretched rubber-band by L is:
(a)
(b)
(c)
(d)
6. A particle is acted by a force F = kx, where k is a +ve constant. Its
potential energy at x = 0 is zero. Which curve correctly represents the
variation of potential energy of the block with respect to x
(a)
(b)
(c)
(d)
7. A particle of mass m is driven by a machine that delivers a constant
power of k watts. If the particle starts from rest the force on the particle
at time t is
(a)
(b)
(c)
(d)
8. A moving body with a mass m
1
 and velocity u strikes a stationary body
of mass m
2
. The masses m
1
 and m
2
  should be in the ratio m
1
/m
2
 so as to
decrease the velocity of the first body to 2u/3 and giving a velocity of v
to m
2
 assuming a perfectly elastic impact. Then the ratio m
1
/m
2
 is
(a) 5
(b)
(c)
(d) 25
9. Two similar springs P and Q have spring constants K
P
 and K
Q
, such that
K
P
 > K
Q
. They are stretched, first by the same amount (case a,) then by
the same force (case b). The work done by the springs W
P
 and W
Q
 are
related as, in case (a) and case (b), respectively
(a) W
P
 = W
Q
 ; W
P
 = W
Q
(b) W
P
 > W
Q
 ; W
Q
 > W
P
(c) W
P
 < W
Q
 ; W
Q
 < W
P
(d) W
P
 = W
Q
 ; W
P
 > W
Q
10. A body is allowed to fall freely under gravity from a height of 10m.  If
it looses 25% of its energy due to impact with the ground, then the
maximum height it rises after one impact is
(a) 2.5m (b) 5.0m (c) 7.5m (d) 8.2m
11. Water falls from a height of 60 m at the rate of 15 kg/s to operate a
turbine. The losses due to frictional force are 10% of energy. How
much power is generated by the turbine?( g = 10 m/s
2
)
(a) 8.1 kW
(b) 10.2 kW
(c) 12.3 kW
(d) 7.0 kW
12. A glass marble dropped from a certain height above the horizontal
surface reaches the surface in time t and then continues to bounce up
and down. The time in which the marble finally comes to rest is
(a) e
n
t
(b) e
2
t
(c)
(d)
13. A block C of mass m is moving with velocity v
0
 and collides elastically
with block A of mass m and connected to another block B of mass 2m
through spring constant k. What is k if x
0
 is compression of spring when
velocity of A and B is same?
`
(a)
(b)
(c)
(d)
14. In the figure shown, a particle of mass m is released from the position A
on a smooth track. When the particle reaches at B, then normal reaction
on it by the track is
(a) mg
(b) 2mg
(c)