# The velocity time graph of a ball of mass 20g moving along a straight line on a long table is given in (figure) How much force does the table exert

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The velocity time graph of a ball of mass 20g moving along a straight line on a long table is given in (figure) How much force does the table exert on the ball to bring it to rest?

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The initial velocity of the ball is 20 cm s^(-1). Due to the frictional force exerted by the table, the velocity of the ball decreases down to zero in 10 s. Thus, u = 20 cm s^(–1), v = 0 cm s^(-1) and t = 10 s. Since the velocity-time graph is a straight line, it is clear that the ball moves with a constant acceleration. The acceleration a is
a=(v-u)/(t)
=0 cm s^(-1) -20 cm s^(-1)//10 s
=-2 cm s^(-2)=-0.02 ms^(-2)
The force exerted on the ball F is , F=ma=(20//1000) kg xx (-0.02ms^(-2))
= -0.0004 N. The negative sign implies that the fricitonal force exerted by the table is opposite to the direction of motion of the ball.