Question

A particle is moving along a straight line. The displacement of the particle becomes zero in a certain time (t > 0). The particle does not undergo any collision.

• A. The acceleration of the particle may be zero always.
• B. The acceleration of the particle may be uniform.
• C. The velocity of the particle must be zero at some instant
• D. The acceleration of the particle must change its direction

Answer 1

Answer: (B), (C)

The acceleration of the particle may be uniform.
The velocity of the particle must be zero at some instant

Since the particle is moving along a straight line and displacement is zero at certain time t>0,so we can deduce that particle has to change its direction and should again pass through the same point so that displacement becomes zero.
Thus the velocity of particle should be zero at some point so that particle can change its direction and acceleration can be uniform i.e opposing motion of the particle.
Acceleration of particle need not change its direction.
Acceleration of particle cannot be zero always because the particle has to change its direction in order for the displacement to be zero.This all happens in the case of objects thrown up and coming down on the surface of earth and the acceleration of the object is nothing but acceleration due to gravity.