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. The velocity attained by the ball is\\
(1) $40 \mathrm{~m}/\mathrm{s}$\\
(2) $20 \mathrm{~m}/\mathrm{s}$\\
(3) $10 \mathrm{~m}/\mathrm{s}$\\
(4) $10\sqrt{30} \mathrm{~m}/\mathrm{s}$