Question

A ball is thrown vertically upwards with an initial velocity of 60m/s. After time t seconds, its height above the ground is given as s=60t-16t2. Find its instantaneous velocity after t seconds. Discuss the specialty about time t=15/8

Answer 1

Have you read a little bit of differential calculus ?

Answer 2

ds/dt gives you the desired instantaneous velocity at t seconds. At t = 15/8 , ds/dt is 0 i.e, the velocity = 0 corresponding to maxima of s. After that the ball starts falling down, as velocity changes direction.