Question

A ball is thrown upward from the ground with an initial speed of 'u'. The ball is at a height of 80m at two times. The time interval being 6s . Find 'u' (take g= 10 m/s^2).

Answer 1

Total time taken in travelling from 80 m instant to 80 m instant again= 2u/g

Let, velocity at 80 m instant is V and total time taken is 6 sec, then,

2V/g=6

V=30 m/s

Now, consider motion from ground to 80m instant,

V^2-U^2=2as.....(i)

Putting the value of V=30 and S=80 in eqn. (i), we get

U=50m/s