Q1. A stone is tied to a rope and attached to a wooden bar which rotates at constant angular velocity. Suddenly the bar is stopped. The stone gets encircled around the bar. What happens to the angular velocity of the stone.
(a) Increases
(b) Decreases
(c) Remains the same
(d) First increases and then decreases
(UPSC Prelims 1984)
Answer: (a) Increases
Explanation: When the bar stops, the stone continues to move due to inertia, and the radius of rotation decreases as it wraps around the bar. According to the conservation of angular momentum, a decrease in radius leads to an increase in angular velocity.
Q2. Ball-bearings are used to reduce the friction by
(a) Reducing the area of contact with the use of metallic balls
(b) Increasing the area of contact with the use of metallic balls
(c) Applying lubricants to the balls used
(d) None of the above
(UPSC Prelims 1985)
Answer: (a) Reducing the area of contact with the use of metallic balls
Explanation: Ball-bearings reduce friction by allowing rolling motion instead of sliding. The metallic balls minimize contact area, thereby reducing resistance and enabling smooth rotation of mechanical parts.