A spherical ball of mass 20 kg is stationary at the top of a hill of height 100 m. It rolls down a smooth surface to the ground then climbs up another hill of height 30 m and finally rolls down to a horizontal base at a height of 20 m above the ground. Find the velocity attained by the ball, when moving at horizontal base.

Options

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

Answer

D

Explanation

Ball starts from the top of a hill which is 100 m high and finally rolls down to a horizontal which is 20 m above the ground, so from the conservation of energy.
`m g(h_1 - h_2) = 1/2 mv^2`
`implies v = sqrt(2g(h_1 - h_2)) = sqrt(2 xx 10 xx (100 - 20)) = sqrt(1600) = 40 m//s`.