Read each staremnt below carefully and state with reasons and expamples if it is true or false ,
(a) with zero speed at an instant may have non-zero accelration at that instant
(b) with zero speed may have non-zero velocity
(c ) with positive speed must have zero accleration
(d) with positive value of acceleration must be speeding up.

Explanation

(a) Ture, when a body is thrown vertically upwards inn the space, then at the highest point, the body has zero speed but has downward acceleration equal to the accelration due to gravity.
(b) false, becomuse velocity is the speed of body in a given direction. When speed is zero, the magnitude of velocity of body is zero, hence velocity is zero.
(c ) True, when a particle is moving along a straight line with a constant speed, its velocity remains constant with time . Therefore, acceleration (= change in velocity //time ) is zero. ltbRgt (d) The statement depends upon the chice of the instant of time taken as origin as origin, when the bdy is moving along a straight line with positive accelration. The velocity of the body at an instant of time (t) is
` v=u +at`
The given statement is not correct if (a) is positive and (u) is negative, at the instant of time taken as origin. Then for all the times before the time for which (v) venishes, there is slowing down of the particle i.e. the speed of the particle keeps on decteasing with time. It happens when body is projected vertically upwards. However the given statement is true if u) is positive and (a) is positive, at the instant of time taken as origin. It is so when the body is falling verticall downwards.