Question

A particle in one-dimensional motion:

• A. with zero speed at an instant may have non-zero acceleration at that instant
• B. with zero speed may have non-zero velocity
• C. with constant speed must have zero acceleration
• D. with positive value of acceleration must be speeding up

Answer 1

The correct option is A with zero speed at an instant may have non-zero acceleration at that instant

(a) Correct. Example, if the ball is in vertically upward motion, i.e., throw vertically upward, then it will be of zero speed at the highest point and an acceleration of 9.8 ms-2 in downward direction.
(b) Incorrect, because speed is the magnitude of velocity.
© Correct, if the particle rebounds instantly with the same speed acceleration will be zero.
Example, Elastic collision of a ball with an elastic floor.
(d) Wrong. Example, if we take the positive direction
of acceleration due to gravity downwards, a ball thrown vertically upwards will have its speed decreasing. However, the statement can be correct if the positive direction of acceleration is along the direction of motion.