Question

A ball of mass 0.4 kg starts rolling on the ground at 20 ms^–1 and comes to a stop after 10s. Calculate the force which stops the ball, assuming it to be constant in magnitude throughout.

Answer 1

 Given m= 0.4 kg, initial velocity u = 20 ms^–1, final velocity v = 0 m s^–1 and t = 10s. So

Here negative sign shows that force on the ball is in a direction opposite to that of its motion.