A spherical ball of mass \(20\mathrm{kg}\) is stationary at the top of a hill of height \(100\mathrm{m}\) . It rolls down a smooth surface to the ground, then climbs up another hill of height \(30\mathrm{m}\) and finally rolls down to a horizontal base at a height of \(20\mathrm{m}\) above the ground. The velocity attained by the ball is