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

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.
s=1/2at²
s=1/2x5x2x2
s=10

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.

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

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
 

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

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.

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.

We can use the principle of conservation of mechanical energy to solve this problem. According to this principle, the potential energy (PE) at the height is converted into kinetic energy (KE) as the fish dives to the ground.

The formula for potential energy is:

PE=mgh

Where:

• m=35 kg
• g=10 m/s^2
• hhh is the height through which the fish dived (which we need to find)

Given that the kinetic energy when the fish hits the ground is equal to the potential energy it had at the starting height:

KE=PE

3500 J=35×10×h

Now solve for h:

3500=350h

h=3500/350=10 m

So, the height through which the fish dived is 10 meters.

The correct answer is:

3. 10 m.

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.

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

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

since kinetic energies are equal

KE₁ = KE₂

mv₁²/2 = 4mv₂²/2

v₁/v₂ = √4/1 = 2:1

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.

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.

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.

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

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.

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. 

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.

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