# Engineering Physics Questions and Answers – Energy

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This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Energy”.

1. A boy carrying a box on his head is walking on a level load from one place to another on a straight road is doing no work. The statement is?
a) Correct
b) Incorrect
c) Partly correct
d) Insufficient data

Explanation: The body applies force on the load in the upward direction. The displacement of the load is in the horizontal direction.

2. Kinetic energy with any reference must be ___________
a) Zero
b) Positive
c) Negative
d) Either negative or positive

Explanation: KE = 1/2 mv2
It is always positive.

3. The kinetic energy of a body becomes four times of its initial value, then new momentum will ___________
a) Become twice its initial value
b) Become thrice its initial value
c) Become four times its initial value
d) Remains constant

Explanation: p = √2mK
p = √(2m×4K) = 2√2mK = 2p
If the kinetic energy of a body becomes four times of its initial value, then new momentum will become twice its initial value.

4. The decrease in potential energy of a ball of mass 20kg, which falls from a height of 50cm, is?
a) 968J
b) 98J
c) 1980J
d) 450J

Explanation: U = mgh
U = 20×9.8×0.50 = 98J.

5. If the water falls from a dam into a turbine wheel 19.6m below, then the velocity of water at the turbine is? (g=9.8m/s)
a) 9.8m/s
b) 19.6m/s
c) 39.2m/s
d) 98m/s

Explanation: Loss in potential energy = Gain in kinetic energy
mgh = 1/2mv2
v = √2gh = √(2×9.8×19.6)=19.6m/s.

6. Momentum is conserved in all collisions but not kinetic energy.
a) True
b) False

Explanation: Momentum is conserved in all collisions but not kinetic energy. Kinetic energy is conserved only inelastic collision.

7. Two particles are seen to collide and move jointly together after the collision. During such a collision, for the total system ___________
a) Neither the mechanical energy nor the linear momentum is conserved
b) Mechanical energy is conserved, but not the linear momentum
c) Both the mechanical energy and the linear momentum are conserved
d) Linear momentum is conserved, but not the mechanical energy

Explanation: The collision is inelastic. Only momentum is conserved and not mechanical energy. There is a loss of kinetic energy in such a collision.

8. In elastic collision, 100% energy transfer takes place when ___________
a) m1=2m2
b) m1 is greater than m2
c) m1 is lesser than m2
d) m1=m2

Explanation: During elastic collision between two equal masses, the velocities get exchanged. Hence energy transfer is maximum when m1=m2.

9. Assertion: In and elastic collision of two billiard balls, the total kinetic energy is conserved during the short time of collision of balls.
Reason: Energy spent against friction does not follow the law of conservation of energy
a) Both assertion and reason are true and the reason is the correct explanation of the assertion
b) Both assertion and reason are true but the reason is not the correct explanation of the assertion
c) Both assertion and reason are false
d) Assertion is true but the reason is false

Explanation: The billiard balls in an elastic collision are in a deformed state. Their total energy is partly kinetic and partly potential. So kinetic energy is less than the total energy spent against friction is dissipated as heat which is not available for doing work.

10. When a body moves with a constant speed along a circle ___________
a) No work is done on it
b) No acceleration is produced in it
c) Its velocity remains constant
d) No force acts on it 