## Rotational Mechanics Conceptual Questions

Here find good conceptual questions on Rotational Mechanics. Rotational mechanics questions can be bit tricky so you need to attempt them carefully.

**Question (1) **If the total external force acting on a rigid body is zero, then

(a) only linear momentum remains constant

(b) only angular momentum remains constant

(c) both linear momentum and angular momentum remains constant

(d) neither linear momentum nor angular momentum remain constant

**Question (2)** A ball of mass M is tied to a string of length L is whirled round in a horizontal plane in a circle of radius R. The speed of the stone is increased beyond the maximum permissible value and the string breaks suddenly; then

(a) the stone will jerk radially outwards

(b) the stone will jerk radially inwards

(c) the stone will fly off tangentially from the instant the string breaks

(d) None of the above

**Question (3)** Which of the following statements is false

(a) During rolling the force of friction acts in the same direction as the direction of motion of the center of mass of the body

(b) The instantaneous speed of the point of contact during rolling is zero

(c) The instantaneous acceleration of the point of contact during rolling is zero

(d) For perfect rolling, work done against friction is zero

**Question (4)** For a particle rotating about a fixed axis with non-uniform angular velocity, there

(a) is only radial acceleration

(b) is only tangential acceleration

(c) is neither radial nor tangential acceleration

(d) are both radial acceleration and tangential acceleration

**Question (5)** The moment of inertia plays the same role in rotational motion as is played in linear motion by

(a) velocity

(b) momentum

(c) energy

(d) mass

**Question (6)** The trajectory of a ‘fixed’ point on the rim of a wheel of a vehicle as the vehicle moves with a constant speed is being observed by an observer fixed on ground. The trajectory, as noted by him will be

(a) a circle coinciding with circumference of the wheel repeating itself

(b) a parabola with vertex at the highest point on the wheel

(c) a straight line parallel to road

(d) a cycloid, repeating itself with every rotation of the wheel

**Question (7)** A jet engine works on the principle of conservation of

(a) mass

(b) energy

(c) linear momentum

(d) Angular momentum

(e) None of the above

**Question (8)** . A rectangular container half full of oil is being carried by a train on a horizontal track. If the train accelerates, the surface of the oil in the container with respect to horizontal surface will

(a) be raised upward from the front

(b) be raised in the middle

(c) be raised upward from the back

(d) remain unchanged

(e) Not sufficient information

**Question (9)** The center of mass of a system of two particles is

(a) on the line joining then and midway between them

(b) on the line joining them at a point whose distance from each particle is proportional to the square of the mass of the particle

(c) on the line joining them and at a point whose distance from each particle is proportional inversely to the mass of that particle

(d) on the line joining them and at a point whose distance from each particle is proportional to the mass of that particle

**Question (10)** Of the two spheres of same size, mass and appearance one is hollow and other is solid. If the two are rolled down an inclined plane simultaneously, then

(a) hollow sphere will reach the bottom first

(b) solid sphere will reach the bottom first

(c) both will reach bottom together

(d) either can reach first depending upon the surface of the plane

**Question (11)** A shell fired from a gun at an angle to the horizontal explodes in mid air. The center of mass of the shell fragments will have

(a) vertically down

(b) horizontally

(c) along the same parabolic path of the unexploded shell

(d) along the tangent to the parabolic path of unexploded shell

**Question (12)** If a particle moves in the x – y plane, its angular momentum

vector is in the

(a) x -direction

(b) z- direction

(c) y -direction

(d) x-y direction

**Question (13)** At a given moment, the total angular momentum of a system of two particles about a certain point is zero. Accordingly we know that the particles

(a) must both be at rest.

(b) must be moving on the same circle in opposite directions.

(c) must be moving on straight perpendicular paths.

(d) must have the same magnitude linear momentum.

(e) None of the above statements are correct

**Question (14)** A particle of mass m and speed v has zero angular momentum with respect to a point Z in space. We know that the particle

(a) will never pass through Z

(b) is moving along a line that is perpendicular to the plane containing it and Z

(c) is moving along a line that passes through Z

(d) must have already passed through point Z

(e) Not sufficient information

**Question (15)** Two initially stationary skaters, of unequal mass( M ,m and M > m) face each other on a frictionless horizontal ice surface. If they push apart, which one of the following statements is true?

(a) The skater (M) experiences twice the magnitude force experienced by the skater(m).

(b) The skater(m) experiences twice the magnitude impulse experienced by the skater(M)

(c) After separation, both skaters have the same speed.

(d) After separation, both skaters have the same kinetic energy.

(e) After separation, both skaters have momentum of equal magnitude but in opposite directions.

**Question (16)**. If the resultant of all the external forces acting on a system of particles is zero, then from an inertial frame , one can surely say that

(a) Linear momentum of the system does not change in time

(b) KE of the system does not change in time

(c) Angular momentum of the system does not change with time

(d)Angular Momentum of the system does not change in time

**Question (17)**. Angular momentum of a single particle moving along with constant speed along circular path

(a)changes in magnitude but remains same in the direction

(b) Remain same in magnitude and direction

(c) remain same in magnitude but changes in direction

(d) is zero

**Question (18)**. A particle is confined to rotate in a circular path decreasing linear speed, then which of the following is correct?

(a) Angular Momentum is conserved

(b) Its spiral towards the center

(c) Its acceleration is towards the center

(d)Only direction of the angular momentum is conserved

**Question (19).** A particle undergoes uniform circular motion. About which point on the plane of the circle, will the angular momentum of the particle remain conserved?

(a) Center of the circle

(b) on the circumference of the circle

(c) inside the circle

(d) Outside the circle

**Question (20).** A cylinder rolls up an inclined plane ,reaches some height and then rolls down (without slipping throughout these motions). The directions of frictional force acting on the cylinder

(a) Up the incline while ascending and down the incline descending

(b) Up the incline while ascending and descending

(c)down the incline while ascending and descending

(d)down the incline while ascending and up the incline descending

**Answers**

1. a

2. c

3.a

4.d

5.d

6.d

7. c

8.c

9.

11. c

12. b

13. e

(A), (B), (C) and (D) are all possible conditions of the particles, but none must be true.

Therefore answer is E.

14. c

15. d

16. a

17.b

18. d

19.a

20. b

ashokIs it possible to get this study material in hindi

physicscatalystHi, I am really sorry we do not have study material in hindi. One trick is you can translate the page through google translate tool but i do not think that you will get the things correctly but you can give it a try.

physicscatalystI have just seen the translation of this page this seems fine to be . for this right click your mouse and see the option for translation.

hope it helped

Elizabeth MendlerIs there answers to this somewhere