question_answer

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                                         [AIEEE 2005]

A) 40 m/s

B) 20 m/s

C) 10 m/s

D) 10V30m/s

Correct Answer: A

Solution :

[a] If all the forces (external) are conservative and there is no external force exerting on the system, then we apply principle of conservation of total mechanical energy of the system.

According to conservation of energy,

or

or