Question

With what speed must a ball be thrown down for it bounce 15m higher than its original level? Neglect any loss of energy in striking the ground.

Answer 1

1/2 mu.u + mgh =mg( h + 10) 



1/2mu.u +mgh=mgh+10mg 


1/2 u.u =10g 


u.u=20g 


u=14

Answer 2

Hey User 

BY Energy conservation law 

mg(h+15) = mgh + 1/2mv²

gh + 15 g = gh + 1/2v²

15g = 1/2v²

30g = v²

v = √30g 

v = √(30 x 9.8)

v = 17.14 m/s