Question

A ball thrown vertically upwards with speed 'u' from the top of a tower reaches the ground in 9 s. Another ball is thrown vertically downwards from the same position with speed 'u', takes 4 s to reach the ground. Calculate the value of 'u' . (Take g=10ms −1
)

Answer 1

Answer:

Explanation:

if ball thrown vertically downwards with same velocity u  

then time = 16/9 sec

height of tower from second

h=1/2at^2

h=5t^2

h=80 m

s=ut+1/2at^2

80=16u/9 + 5(256/81 )

80 = 16u/9 + 15.8

64.2 = 16u/9

u=36.1125

alter method

-s=ut-1/2at^2

s=1/2at^2

s=80 m

-80 = 9u - 405

u=36.11