A spherical ball of mass `20kg` is stationary at the top of a hill of height `100m` , it rolls down a smooth surface to the ground , then climbs up another bill of height of `30 m` and final rolls down to a horizontal base at a height of `20 m` about the ground . The velocity attained by the ball is

Options

A. `20 m//s `
B. `40 m//s`
C. `10 sqrt(30) m//s`
D. `10 m//s `

Answer

B

Explanation

(b)
Loss in potential energy = gain in kinetic energy
`m xx g xx 80 = (1)/(2) m nu^(2) , 10 xx 80 = (1)/(2) nu^(2) `
`nu^(2) = 1600 `or` nu = 40 m//s `