Question

The velocity of a particle is zero at time $t=2s$ , then

• A. displacement must be zero in the interval $t=0$ to $t=2s.$
• B. acceleration may be zero at $t=2s.$
• C. velocity must be zero for $t>2s.$
• D. acceleration must be zero at $t=2s.$

Answer 1

Answer: (B)

Let us consider an example in which particle is projected vertically upwards from ground at $t=0$ and it reaches the highest point at $t=2s$ .
Then, at that instant $(t=2s)$ velocity $v=0$ , but acceleration $=-g$ .
Here, displacement is non zero for the duration $t=0tot=2s$ . For $t>2s$ the ball again acquires velocity. In this example option $(1),(3)$ and $(4)$ are incorrect.
Let us consider another example in which a particle is moving on a horizontal plane and it comes to rest permanently at $t=1s$ , then this is one of the special case in which acceleration of the particle is zero at $t=2s$ .