Question

A ball is dropped from the top of an 80 m high tower After 2 s another ball is thrown downwards from the tower. Both the balls reach the ground simultaneously. The initial speed of the second ball is
A. `10 m//s`
B. `20 m//s`
C. `30 m//s`
D. `40 m//s`

Answer 1

Correct Answer - C
Let the first ball reaches the ground after time t, the second ball will take time `(t-2)`.
`80=1/2g t^(2)impliest=4 s`
Let u: initial velocity of the second ball
`80=u(t-2)+1/2g (t-2)^(2)`
`=u(4-2)=1/2xx10(4-2)^(2)`
`=2u+20`
`u=30 m//s`