Question

A ball thrown vertically upwards with a speed
'u' from the top of a tower reaches the ground in 9 second. Another ball is thrown vertically downward from the same position with same speed u takes 4 seconds to reach the ground. Calculate the value of u. (g=10m/second square​

Answer 1

Answer:

Let down be the positive direction

H = -u * t1 + 1/2 g t1^2 = -9 u + 5 * 81 = -9 u + 405

H = u * t2 + 1/2 g t2^2 = 4u + 5 * 16

-9 u + 405 = 4 u + 80

13 u = 325

u = 25 m/s