Lakhmir Singh & Manjit Kaur Test: Work & Energy

# Lakhmir Singh & Manjit Kaur Test: Work & Energy - Class 9

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## 20 Questions MCQ Test Science Class 9 - Lakhmir Singh & Manjit Kaur Test: Work & Energy

Lakhmir Singh & Manjit Kaur Test: Work & Energy for Class 9 2023 is part of Science Class 9 preparation. The Lakhmir Singh & Manjit Kaur Test: Work & Energy questions and answers have been prepared according to the Class 9 exam syllabus.The Lakhmir Singh & Manjit Kaur Test: Work & Energy MCQs are made for Class 9 2023 Exam. Find important definitions, questions, notes, meanings, examples, exercises, MCQs and online tests for Lakhmir Singh & Manjit Kaur Test: Work & Energy below.
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Lakhmir Singh & Manjit Kaur Test: Work & Energy - 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?​

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 1

The Kinetic energy acquired by an object that is acted upon by a force is equal to the work done by the force. The work done by the force is equal to the force times the distance the object moved against the force. Therefore, in this case the Kinetic energy acquired by the body is equal to 25 N x 10 m = 250 J.

Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 2

### A freely falling body during its fall will have

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 2
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.
Lakhmir Singh & Manjit Kaur Test: Work & 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​

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 3
P.E. = mghtherefore m = P.E. / gh =( 2250/ (9.8× 3.4)) = (2250/33.32) kg = 67.5 kg . ANS.
Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 4

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

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 4

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

Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 5

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

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 5

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

Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 6

Elastic potential energy of a body can be achieved by

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 6
Elastic Potential Energy:
Elastic potential energy is the energy stored in an elastic object when work is done upon it to compress or stretch it. It is a form of potential energy that is associated with the deformations of elastic materials.
Methods to Achieve Elastic Potential Energy:
The elastic potential energy of a body can be achieved by:
1. Compressing the Body:
- When a force is applied to compress a spring or any elastic object, work is done against the restoring force.
- The energy is stored in the object in the form of potential energy.
- For example, a compressed spring or a stretched rubber band.
2. Stretching the Body:
- When a force is applied to stretch an elastic object, work is done to overcome the elastic force.
- The energy is stored in the object as potential energy.
- For example, a stretched rubber band or a stretched balloon.
Incorrect Options:
A. Setting it into motion: This option does not directly result in the storage of elastic potential energy.
B. Raising the body to a height: This option refers to gravitational potential energy, not elastic potential energy.
C. Using an elastic band to tie the body: Tying a body with an elastic band does not directly result in the storage of elastic potential energy.
Conclusion:
To achieve elastic potential energy, the body needs to be compressed or stretched. This can be done by applying a force to the object, such as compressing a spring or stretching a rubber band. The potential energy is stored in the object due to the deformations caused by the applied force.
Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 7

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

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 7

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.

Lakhmir Singh & Manjit Kaur Test: Work & Energy - 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

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 8

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

Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 9

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

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 9

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.

Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 10

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

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 10

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

Lakhmir Singh & Manjit Kaur Test: Work & Energy - 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:

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 11
Change in KE is workdone by work energy theoream 60-12=48j
Lakhmir Singh & Manjit Kaur Test: Work & Energy - 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 :

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 12

since kinetic energies are equal

KE1 = KE2

mv12/2 = 4mv22/2

v1/v2 = √4/1 = 2:1

Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 13

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

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 13

To determine the change in kinetic energy when the speed of an object doubles, we can refer to the equation for kinetic energy:
Kinetic Energy (KE) = 1/2 * mass * velocity^2
1. Initial kinetic energy: Let the initial speed of the object be "v" and its initial kinetic energy be "KEi".
2. Final kinetic energy: When the speed of the object doubles, its new speed becomes "2v". The final kinetic energy can be denoted as "KEf".
3. Comparing initial and final kinetic energies:
- Initial kinetic energy: KEi = 1/2 * mass * v^2
- Final kinetic energy: KEf = 1/2 * mass * (2v)^2 = 1/2 * mass * 4v^2
4. Simplifying the final kinetic energy expression:
KEf = 1/2 * mass * 4v^2 = 2 * (1/2 * mass * v^2) = 2 * KEi
Therefore, the final kinetic energy is double the initial kinetic energy when the speed of an object doubles. Hence, the correct answer is B: four times.
Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 14

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

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 14

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.

Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 15

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

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 15

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.

Lakhmir Singh & Manjit Kaur Test: Work & Energy - 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:

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 16
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
Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 17

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

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 17

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.

Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 18

A body at rest cannot have:

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 18

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.

Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 19

Potential energy is energy possessed by an object due to its

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 19

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.

Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 20

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

Detailed Solution for Lakhmir Singh & Manjit Kaur Test: Work & Energy - Question 20

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

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