# Machine Kinematics Questions and Answers – Kinetics of Motion

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This set of Machine Kinematics Multiple Choice Questions & Answers (MCQs) focuses on “Kinetics of Motion”.

1. The force which acts along the radius of a circle and directed ____________ the centre of the circle is known as centripetal force.
a) away from
b) towards
c) at the
d) none of the mentioned

Explanation: Centripetal force acts radially inwards and is essential for circular motion.

2. The unit of mass moment of inertia in S.I. units is
a) m4
b) kgf-m-s2
c) kg-m2
d) N-m

Explanation: Moment of inertia is the distance, from a give reference, where the whole mass of body is assumed to be concentrated to give the same value of I. The unit of mass moment of inertia in S.I. units is kg-m2.

3. Joule is a unit of
a) force
b) work
c) power
d) none of the mentioned

Explanation: In S.I. system of units, the practical unit of work is N-m. It is the work done by a force of 1 newton, when it displaces a body through 1 metre. The work of 1 N-m is known as joule (briefly written as J ) such that 1 N-m = 1 J.
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4. The energy possessed by a body, for doing work by virtue of its position, is called
a) potential energy
b) kinetic energy
c) electrical energy
d) chemical energy

Explanation: Potential energy is the energy possessed by a body for doing work, by virtue of its position.
Kinetic energy is the energy possessed by a body, for doing work, by virtue of its mass and velocity of motion.

5. When a body of mass moment of inertia I (about a given axis) is rotated about that axis with an angular velocity, then the kinetic energy of rotation is
a) 0.5 I.ω
b) I.ω
c) 0.5 I.ω2
d) I.ω2

Explanation: When a body of mass moment of inertia I (about a given axis) is rotated about that axis, with an angular velocity ω, then it possesses some kinetic energy. In this case,
Kinetic energy of rotation = 1/ 2I.ω2

When a body has both linear and angular motions e.g. in the locomotive driving wheels and wheels of a moving car, then the total kinetic energy of the body is equal to the sum of kinetic energies of translation and rotation.
∴ Total kinetic energy = 1/ 2mv2 +1/ 2I.ω2

6. The wheels of a moving car possess
a) potential energy only
b) kinetic energy of translation only
c) kinetic energy of rotation only
d) kinetic energy of translation and rotation both.

Explanation: in the locomotive driving wheels and wheels of a moving car, then the total kinetic energy of the body is equal to the sum of kinetic energies of translation and rotation.

7. The bodies which rebound after impact are called
a) inelastic bodies
b) elastic bodies
c) solid bodies
d) none of the mentioned

Explanation: The bodies, which rebound after impact are called elastic bodies and the bodies which does not rebound at all after its impact are called inelastic bodies.

8. The coefficient of restitution for inelastic bodies is
a) zero
b) between zero and one
c) one
d) more than one

Explanation: The process of regaining the original shape is called restitution. Inelastic bodies can not regain their original shapes. Therefore their coefficient of restitution is zero.

9. Which of the following statement is correct ?
a) The kinetic energy of a body during impact remains constant.
b) The kinetic energy of a body before impact is equal to the kinetic energy of a body after impact.
c) The kinetic energy of a body before impact is less than the kinetic energy of a body after impact.
d) The kinetic energy of a body before impact is more than the kinetic energy of a body after impact.

Explanation: Total kinetic energy of the system before impact,
E1 = 1/2 m1 (u1)2 + 1/2 m2 (u2)2

When the two bodies move with the same velocity v after impact, then
Kinetic energy of the system after impact,

E2= 1/2( m1 + m2) v2

∴ Loss of kinetic energy during impact,
EL = E1 – E2

10. A body of mass m moving with a constant velocity v strikes another body of same mass m moving with same velocity but in opposite direction. The common velocity of both the bodies after collision is
a) v
b) 2 v
c) 4 v
d) 8 v

Explanation: If the body will move in opposite direction a negative sign would be there.
We know that Common velocity = V12
Here both the velocities are same.
Therefore Common velocity = V – (-V)
= V + V = 2V

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