## Motion in a Plane Questions and Answers Part-2

1. A particle moves with constant angular velocity in a circle. During the motion its
a) Energy is conserved
b) Momentum is conserved
c) Energy and momentum both are conserved
d) None of the above is conserved

Explanation: In uniform circular motion (constant angular velocity) kinetic energy remains constant but due to change in velocity of particle its momentum varies.

2. A stone tied to a string is rotated in a circle. If the string is cut, the stone flies away from the circle because
a) A centrifugal force acts on the stone
b) A centripetal force acts on the stone
c) Of its inertia
d) Reaction of the centripetal force

Explanation: Of its inertia

3. A body is revolving with a constant speed along a circle. If its direction of motion is reversed but the speed remains the same, then which of the following statement is true
a) The centripetal force will not suffer any change in magnitude
b) The centripetal force will have its direction reversed
c) The centripetal force will not suffer any change in direction
d) Both a and c

Explanation: Centripetal force = $\frac{mv^{2}}{r}$ and is directed always towards the centre of circle. Sense of rotation does not affect magnitude and direction of this centripetal force.

4. When a body moves with a constant speed along a circle
a) No work is done on it
b) No acceleration is produced in the body
c) No force acts on the body
d) Its velocity remains constant

Explanation: When speed is constant in circular motion, it means work done by centripetal force is zero.

5. A body of mass m moves in a circular path with uniform angular velocity. The motion of the body has constant
a) Acceleration
b) Velocity
c) Momentum
d) Kinetic energy

Explanation: Kinetic energy

6. On a railway curve, the outside rail is laid higher than the inside one so that resultant force exerted on the wheels of the rail car by the tops of the rails will
a) Have a horizontal inward component
b) Be vertical
c) Equilibriate the centripetal force
d) Be decreased

Explanation: This horizontal inward component provides required centripetal force

7. If the overbridge is concave instead of being convex, the thrust on the road at the lowest position will be
a) $mg+\frac{mv^{2}}{r}$
b) $mg-\frac{mv^{2}}{r}$
c) $\frac{m^{2}v^{2}g}{r}$
d) $\frac{v^{2}g}{r}$

Explanation: 8. A cyclist taking turn bends inwards while a car passenger taking same turn is thrown outwards. The reason is
a) Car is heavier than cycle
b) Car has four wheels while cycle has only two
c) Difference in the speed of the two
d) Cyclist has to counteract the centrifugal force while in the case of car only the passenger is thrown by this force

Explanation: Cyclist has to counteract the centrifugal force while in the case of car only the passenger is thrown by this force

9. A car sometimes overturns while taking a turn. When it overturns, it is
a) The inner wheel which leaves the ground first
b) The outer wheel which leaves the ground first
c) Both the wheels leave the ground simultaneously
d) Either wheel leaves the ground first