Question

A piece of stone is thrown vertically upwards. It reaches the maximum height in 3 seconds. If the acceleration of the stone be 9.8 m/s² directed towards the ground, calculate the initial velocity of the stone with which it is thrown upwards

Answer 1

v (final velocity) = 0 m/s
u (initial velocity) = ?
a (acceleration due to gravity i.e.,  g) = 9.8m/s²
t (time) = 3 sec
v  = u + gt
0 = u + 9.8 × 3
0 = u + 29.4
u  = −29.4m/s   
Note - Answer is in negative i.e. −29.4m/s, as it is directed opposite to the acceleration due to gravity and we have taken the motion along acceleration due to gravity as positive.
Answer: 29.4m/s