# Engineering Physics Questions and Answers – Moment of Inertia

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

1. A gun fires a bullet of mass 50g with a velocity of 30m/s. Because of this, the gun is pushed back with a velocity of 1m/s. The mass of the gun is?
a) 5.5kg
b) 3.5kg
c) 1.5kg
d) 0.5kg

Explanation: By conservation of momentum, MV = mv
M = mv/V = 1.5kg.

2. A body of mass 5kg is raised vertically to a eight of 10m by a force of 170N. The velocity of the body at this height will be ___________
a) 37m/s
b) 22m/s
c) 15m/s
d) 9.8m/s

Explanation: W = Gain in potential energy+Gain in kinetic energy
Fh = mgh + 1/2 mv2
170×10=5×10×10+1/2×5×v2
v = √480 = 22m/s.

3. A position dependent force, F = 7-2x+3x2-N acts on a small body of mass 2kg and displaces it from x = 0 to x = 5m. The work done in joules is ___________
a) 135
b) 270
c) 35
d) 70

Explanation: W = ∫Fdx = $$\int_0^5 (7-2x+3x^2)dx = [7x-x^2+x^3]_0^5$$
W = 35-25+125=135J.

4. A particle of mass M is moving in a horizontal circle of radius R with uniform speed v. When it moves from one point to a diametrically opposite point, its ___________
a) Kinetic energy changes by (Mv)2/4
b) Momentum does not change
c) Momentum changes by 2Mv
d) Kinetic energy changes by (Mv)2

Explanation: At any two diametrically opposite points, velocities of the particle have the same magnitude but opposite directions. Therefore change in momentum = Mv-(-MV)=2Mv.

5. Two identical balls A and B collide head on elastically. If velocities of A and B, before the collision are +0.5m/s and -0.3m/s respectively, then the velocities after the collision, are ___________
a) -0.5m/s and +0.3m/s
b) +0.5m/s and +0.3m/s
c) +0.3m/s and -0.5m/s
d) -0.3m/s and +0.5m/s

Explanation: In an elastic collision between two bodies of equal masses, velocities get exchanges after collision. vA=-0.3m/s and vB=+0.5m/s.

6. The kinetic energy acquires by a mass m in travelling distance d, starting from rest, under the action of a constant force is directly proportional to ___________
a) m
b) m0
c) √m
d) 1/√m

Explanation: v2-u2=2as
v2-0=2×F/m×d = 2Fd/m
Kinetic energy = 1/2 mv2=1/2 m×2Fd/m = Fd
Hence, kinetic energy does not depend on m or it is directly proportional to m0.

7. A simple pendulum hanging freely and at rest is vertical because in that position ___________
a) Kinetic energy is zero
b) Potential energy is zero
c) Kinetic energy is minimum
d) Potential energy is minimum

Explanation: In the position of equilibrium, the potential energy of the simple pendulum is minimum. Therefore a simple pendulum hanging freely and at rest is vertical because in that position potential energy is minimum.

8. A bullet is fired and gets embedded in a block kept on the table. If a table is frictionless, then ___________
a) Kinetic energy gets conserved
b) Potential energy gets conserved
c) Momentum gets conserved
d) Kinetic energy and potential energy gets conserved

Explanation: Only momentum gets conserved when a bullet is fired and gets embedded in a block kept on a frictionless table. Some kinetic energy is lost when the bullet penetrates the block.

9. A ball moves in a frictionless inclined table without slipping. The work done by the table surface on the ball is ___________
a) Positive
b) Negative
c) Zero
d) Infinity

Explanation: Motion without slipping implies pure rolling. During pure rolling work done by friction force is zero.

10. Assertion: When a body moves along a circular path, no work is done by the centripetal force.
Reason: The centripetal force is used on moving the body along the circular path and hence no work is done.
a) Both assertion and reason are true and reason is the correct explanation of the assertion
b) Both assertion and reason are true but the reason is not the correct explanation of assertion
c) Assertion is true but reason is false
d) Both assertion and reason are false