Question

Read each statement below carefully and state with reasons and examples, if it is true or false; A particle in one-dimensional motion

1. with zero speed at an instant may have non-zero acceleration at that instant

2. with zero speed may have non-zero velocity,

3. with constant speed must have zero acceleration,

4. with positive value of acceleration must be speeding up.

Answer 1

1. True:

Consider a ball thrown vertically, upward. At the highest point, the speed is zero but the acceleration of the ball is non-zero (9.8ms^-2 vertically downwards). Acceleration does not depend on instantaneous speed.

2. False:

Since the magnitude of velocity is speed, a body with zero speed must have zero velocity.

3. True:

In the case of a body rebounding with the same speed, the acceleration at the time of impact is infinite, which is not practical physically.

4. False:

This depends on the chosen positive direction. The statement is true when the direction of motion and acceleration are along the chosen positive direction.