Question

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 and 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

• A. 40 ms^-1
• B. 20 ms^-1
• C. 10 ms^-1
• D. 10$\sqrt{30}$ms^-1

Answer 1

Answer: (A)

40 ms^-1

Answer 2

mgh = $\frac{1}{2}$ mv² or v = $\sqrt{2gh} = \sqrt{2 \times 10 \times 80}$ = 40 ms^-1.