System of Particles and Rotational Motion

 

 MCQs type questions and their answer. 

1. Moment of inertia depends on
(a) Distribution of particles
(b) Mass
(c) Position of axis of rotation
(d) All of these 

2. If a body is rotating about an axis, passing through its centre of mass then its angular momentum is directed along its
(a) Radius
(b) Tangent
(c) Circumference
(d) Axis of rotation

3. A particle moves on a circular path with decreasing speed. Choose the correct statement.
(a) Angular momentum remains constant.
(b) Acceleration is towards the centre.
(c) Particle moves on a spiral path with decreasing radius.
(d) The direction of angular momentum remains constant.

4. The centre of mass of a body
(a) lies always on the surface of the body
(b) lies always inside the body
(c) may lie within, outside on the surface of the body
(d) lies always outside the body

5. The position of centre of mass of a system of particles does not depend upon the
(a) relative distance between the particles 
(b) position of the particles
(c) symmetry of the body
(d) mass of particles

6. If the resultant of all external forces is zero, then velocity of centre of mass will be
(a) zero 
(b) neither (a) nor (b)
(c) constant
(d) either (a) or (b)

7. Angular velocity of each particle of a rotating rigid body about axis of rotation is
(a) same 
(b) different
(c) depends on relative position
(d) None of these

8. Product of moment of inertia and angular acceleration is called:
(a) angular momentum
(b) moment of force
(c) force
(d) work

9. In absence of external force, velocity of the centre of mass:
(a) is zero
(b) will remain constant
(c) will increase
(d) will decrease

10. Which of following quantities remains constant in planetary motion?
(a) kinetic energy
(b) potential energy
(c) linear momentum
(d) angular momentum

Short type questions and their answer. 

Q1.  Why the handle of screw driver is made wide?

Ans: Moment of force τ = F x r. When r is more then for small value of F, τ can be obtained more. This is why the handle of screw driver is made wide.

Q2. A person is sitting on a rotating chair with his arms extended what will happen if he closes his arms?

Ans: On closing his arms, his moment of inertia will decrease, therefore according the of conservation of angular momentum (L = I.ω = constant), his angular velocity of rotation will increase.

Q3. On what factors depends the moment of inertia of a body?

Ans: (i) On axis of rotation (ii) On the distance of mass from axis of rotation.

Q4. The wheels of vehicles are made hollow at centre and thick at circumference; why?

Ans: On doing so, the moment of inertia of the wheel increase and hence amount of rotational energy ER = 1212 Iω² increases and it behaves as flywheel.