A particle in one-dimensional motion. with zero speed at an instant may have non-zero acceleration at that instant,

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

2. False

3. True

4. False

For (1), consider a ball thrown up. At the highest point, speed is zero but the acceleration is non-zero, 

For (2), if a particle has non-zero velocity, it must have speed, 

For (3), if the particle rebounds instantly with the same speed, it implies infinite acceleration which is physically impossible. 

For (4), true only when the chosen positive direction is along the direction of motion.