Question

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

(a) 10m/s

(b) 10√30m/s

(c) 40m/s

(d) 20m/s

I have been asked this question in class test.

I'm obligated to ask this question of Work Done in portion Kinematics of Engineering Physics I

Answer 1

Correct answer is (c) 40m/s

The explanation: Total energy at 100m height = Total energy at 20m height

mgh1= mgh2 + 1/2 mv^2

v = √(2g(h1-h2)) = √(2×10×(100-20)) = 40m/s.