The velocity time graph of a ball moving on the surface of a floor is shown in figure. Find the force acting on the ball if the mass of the ball is 50g.

Explanation

The velocity time graph shows that velocity of the ball at t=0 is `30 ms^-1`
That is, initial velocity of the ball `u=30 ms^-1`
The velocity of the ball at t=6 is zero.
That is final velocity of the ball v=0
Step 1: Acceleration of the ball
`a=(v-u)/t=(0-30 ms^-1)/(6s)=5ms^-2`
Negative sign shows that the motion of the ball is retarded
Step 2: Also mass of ball
`m=50 g=50/1000=1/20 kg`
Force acting on the ball F=ma
`=(1/20 kg)(-5 ms^-2)=-0.25 kg ms^-2`
=`-0.25 N`
Negative sign shows that the force is acting on the ball in a direction opposite to the direction of the motion of the ball. Such force is known as retarding force or opposite force.