A uniform motion of a car along a circular path experiences
- (a)a change in speed due to a change in its direction of motion.
- (b)a change in velocity due to a change in its direction of motion.
- (c)a change in momentum due to no change in its direction of motion.
- (d)a constant momentum due to a change in its direction of motion.
Correct — B, a change in velocity due to a change in its direction of motion. In uniform circular motion the speed is constant, but velocity is a vector that includes direction, and the direction changes continuously along the circle, so the velocity keeps changing. That changing velocity means the car is accelerating, with a centripetal acceleration directed to the centre, even though its speedometer reading stays fixed. Speed itself does not change, so any option claiming a change in speed is wrong.
- (a)a change in speed due to a change in its direction of motion. — The motion is described as uniform, so the speed is constant; only the direction, and hence the velocity, changes.
- (c)a change in momentum due to no change in its direction of motion. — The direction does change all along a circle, so the stated premise is false; momentum changes precisely because the direction changes.
- (d)a constant momentum due to a change in its direction of motion. — Momentum is mass times velocity, a vector, so as the velocity's direction changes the momentum is not constant.
Uniform circular motion is motion along a circle at constant speed. Because velocity is a vector, the continuous change in direction means the velocity keeps changing even though the speed is fixed, so the body is accelerating and needs a centripetal force directed toward the centre.
The key is that uniform fixes the speed but not the direction. Since velocity and momentum are both vectors, a changing direction changes both even at constant speed, which is why circular motion requires a centripetal force.
- Speed is a scalar, while velocity is a vector with both magnitude and direction.
- In uniform circular motion the speed is constant but the direction, and so the velocity, changes continuously.
- A changing velocity means the body is accelerating, with a centripetal acceleration directed to the centre.
- Momentum, being mass times velocity, also changes as the direction changes.
- Equating constant speed with constant velocity.
- Thinking no force acts because the speed is steady.
Asked what changes for a body in uniform circular motion; it is the velocity, through its direction, not the speed.
No directly related past PYQ was found.
- practice — not a real PYQ
A body moves in a circle at constant speed. Which quantity remains constant?
- (a)velocity
- (b)speed
- (c)momentum
- (d)acceleration
Answer(b) speed — velocity, momentum and acceleration keep changing with direction.
- practice — not a real PYQ
Uniform circular motion is accelerated motion because
- (a)its speed changes
- (b)its direction, and hence velocity, changes
- (c)no force acts on it
- (d)its mass changes
Answer(b) its direction, and hence velocity, changes.