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

Answer

A

Explanation

Energy conservation , K.E = P.E
`1/2mv^(2) =mgh`
`v = sqrt(2gh) = sqrt((2xx10 xx 80) = 40 `m/s