Test: Work & Energy - 3


20 Questions MCQ Test NCERT Textbooks (Class 6 to Class 12) | Test: Work & Energy - 3


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QUESTION: 1

A body is acted upon by a force 25 N acquires of 2.5 ms-2 and covers a distance of the force. If the body starts from rest, the Kinetic energy acquired by it is?​

Solution:
QUESTION: 2

A freely falling body during its fall will have

Solution: Object Falling from Rest. As an object falls from rest, its gravitational potential energy is converted to kinetic energy. Conservation of energy as a tool permits the calculation of the velocity just before it hits the surface. K.E. = J, which is of course equal to its initial potential energy.
QUESTION: 3

A boy climbs on to a wall that is 3.4 m high and gains 2250 J of potential energy. What is the mass of the boy? Take g = 9.8 m/Sec2

Solution: P.E. = mghtherefore m = P.E. / gh =( 2250/ (9.8× 3.4)) = (2250/33.32) kg = 67.5 kg . ANS.
QUESTION: 4

A body of mass 4 kg has a momentum of 25 kg m/s, its K.E. is:

Solution:

The correct answer is B asMomentum = mass × velocity
4 = 25 × v
V = 4/25
V = 6.25

To find the kinetic energy ,
KE = 1/2 m v^2
= 1/2 × 25 ×6.25x6.25
= 78.12 J
 

QUESTION: 5

What happens to K.E. of a body when 3/4 th of mass is removed and its velocity is doubled?

Solution:

The correct answer is B as
 let the mass=m
then, m-3/4m=m/4
and velocity=2v
kinetic energy=1/2×mv2
=1/2×m/4×(2v2)
=1/2×m/4×4v2
=1/2mv2

QUESTION: 6

Elastic potential energy of a body can be achieved by

Solution:
QUESTION: 7

If the velocity of a moving car is halved, its kinetic energy would

Solution:

Kinetic Energy = (1/2) mv2.

If the velocity of a body is halved, its kinetic energy becomes one fourth as kinetic energy is directly proportional to velocity squared.

QUESTION: 8

A fish with weight 35 kg dives and hits the ground (zero height) with kinetic energy equal to 3500J. Find the height through which fish dived. Take g = 10 m/s2

Solution:

Using the consersative law of 
Energy formula
Change in potential energy =kinetic energy
 M .g. h = 3500 J
35 . 10.h = 3500
h=10m

QUESTION: 9

Which of the following is not an example of potential energy?

Solution:

The correct option is D.
A moving car is an example of kinetic energy whereas water stored in a dam, compressed spring and stretched rubber band are examples of potential energy.

QUESTION: 10

How fast should a person with mass 50kg walk so that his kinetic energy is 625 J ?

Solution:

K.E = 0.5mv²
v = √(2K.E / m)
= √(2 × 625 Joule / 50 kg)
= √(625 Joule / 25 kg)
= 5 m/s...

QUESTION: 11

The kinetic energy of a body changes from 12 J to 60 J due to the action of a force of 5N on an object of mass 4 kg. The work done by the force is:

Solution: Change in KE is workdone by work energy theoream 60-12=48j
QUESTION: 12

Two bodies of masses m and 4 m are moving with equal kinetic energy. The ratio of velocities with which they are traveling is :

Solution:

since kinetic energies are equal

KE1 = KE2

mv12/2 = 4mv22/2

v1/v2 = √4/1 = 2:1

QUESTION: 13

If the speed of an object doubles, its kinetic energy becomes

Solution:
QUESTION: 14

If two bodies of different masses have the same K.E. then the relation between momentum and mass will be:

Solution:

KE = K = 1 /2( mv2
We know, p = mv
⇒ K = p2 / 2m
 p2  =  2Km
As, KE is Same, ie . Constant, momentum would be directly proportional to the square root of mass.

QUESTION: 15

1 J is the energy required to do ____ of work.

Solution:

One joule =1 newton x 1 meter

since one joule refers to the energy transferred to an object when a force of one newton acts on a body in the direction of motion through a distance of one meter.

QUESTION: 16

A body of mass 44 kg is moving at a velocity of 10 m/s is brought to rest in 10mins, the work done is:

Solution: Mass (m)- 44 kg initial velocity (u) - 10m/s final velocity (v) - 0 time (t)- 10min =600s At first, acceleration (a) = v-u/t =0-10/600 = -1/60m per sec square using 2nd equation of motion s = ut +1/2at^2 s = 10*600 + 1/2*(-1/60*600*600) s=3000m Now, 2nd law of motion Force = ma = 44*(-1/60)=-11/15 N finally, work done=F*s=-11/15*3000= -22000J
QUESTION: 17

For an object to have gravitational potential energy only, it must be

Solution:

The correct option is D.
An object possesses gravitational potential energy if it is positioned at a height above (or below) the zero height. An object possesses elastic potential energy if it is at a position on an elastic medium other than the equilibrium position.

QUESTION: 18

A body at rest cannot have:

Solution:

In physics the Kinetic energy (KE) of an object is the energy that it possesses due to its motion. It is defined as the work needed to accelerate a body of a given mass from rest to its stated velocity. 

QUESTION: 19

Potential energy is energy possessed by an object due to its

Solution:

The correct option is Option C.
Potential energy is the energy that is stored in an object due to its position relative to some zero position. An object possesses gravitational potential energy if it is positioned at a height above (or below) the zero height.

QUESTION: 20

Which of the following produces energy because of temperature difference at various levels in ocean.      

Solution:

The correct option is C.
 Both will have the same kinetic energy.
 

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