# Engineering Physics Questions and Answers – Translational and Rotational Motion

This set of Engineering Physics Multiple Choice Questions & Answers (MCQs) focuses on “Translational and Rotational Motion”.

1. Two racing cars of masses m1 and m2 are moving in circles of radii r1 and r2 respectively. Their speeds are such that each makes a complete circle in the same time t. The ratio of the angular speeds of the first two to the second car will be ____________
a) 1:1
b) r1:r2
c) m1:m2
d) m1 m2:r1 r2

Explanation: ω=v/r=2π/T
As both cars take some time for one revolution, so ω is same for both the cars.

2. A flywheel is attached to an engine to ___________
a) Increase its speed
b) Decrease its speed
c) Help in overcoming the dead point
d) Decrease its energy

Explanation: Due to its large inertia of motion, a flywheel helps the engine to overcome the dead points.

3. Three identical metal balls, each of the radius r are placed touching each other on a horizontal surface such that an equilateral triangle is formed when centres of three balls are joined. The centre of the mass of the system is located at ___________
a) Line joining centres of any two balls
b) Centre of one of the balls
c) Horizontal surface
d) Point of intersection of the medians

Explanation: The centre of mass of the system lies at the point of intersection of the medians that is at the centroid of the equilateral triangle.

4. A solid sphere of radius R is placed on smooth horizontal surface. A horizontal force F is applied at height h from the lowest point. For the maximum acceleration of the centre of mass, which is correct?
a) h=R
b) h=2R
c) h=0
d) no relation between h and R

Explanation: The smooth horizontal surface does not provide any friction. The sphere does not roll. Hence the acceleration of centre of mass of the sphere is independent of the position of the applies force. There is no relation between h and R.

5. Statement 1: The earth is slowing down and as a result, the moon is coming nearer to it.
Statement 2: The angular momentum of the earth-moon system is not conserved.
a) Both statement 1 and 2 are true and statement2 is the correct explanation of the statement1
b) Both statement 1 and 2 are true but statement 2 is not the correct explanation of the statement1
c) Statement 1 is true but statement 2 is false
d) Statement 1 and 2 are false

Explanation: Both the assertion and reason are false. The earth is not slowing down. The angular momentum of the earth-moon system is conserved.
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6. Statement 1: If ice caps of the pole melt, the day length will shorten.
Statement 2: Ice flows towards the equator and decreases the moment of inertia of the earth and hence increases the frequency of rotation of the earth.
a) Both statement 1 and 2 are true and statement2 is the correct explanation of statement 1
b) Both statement 1 and 2 are true but statement 2 is not the correct explanation of statement 1
c) Statement 1 is true but statement 2 is false
d) Statement 1 and 2 are false

Explanation: Both the assertion and reason are false. As the polar ice melts, water so formed flows towards the equator. This increases the moment of inertia. To conserve angular momentum, frequency of rotation decreases and the day length becomes longer.

7. The direction of angular velocity vector is along ___________
a) The tangent to the circular path
d) The axis of rotation

Explanation: If we wrap the right hand around the axis of rotation with the fingers pointing in the direction of rotation, then the thumb points in the direction of angular velocity.

8. The motion of planets in the solar system is an example of the conservation of ___________
a) Mass
b) Linear momentum
c) Angular momentum
d) Energy

Explanation: The motion of planets around the sun is an example of the conservation of angular momentum.

9. A body of mass M while falling vertically downwards under gravity breaks into two parts, a body B of mass 1/3 M and body C of mass 2/3 M. The centre of mass of bodies B and C taken together shifts compared to that of body A towards ___________
a) Body C
b) Body B
c) Depends on the height of braking
d) Does not shift

Explanation: The centre of mass bodies B and C does not shift compared to body A. It continues to move vertically downwards under the effect of gravity. This is because there is no new external force acting on the system.

10. The instantaneous acceleration of the point of contact during rolling is zero.
a) True
b) False

Explanation: As the body is rotating, its instantaneous acceleration cannot be zero.

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