The velocity - time graph of a ball of mass 25g moving on road is as given below:
(a) how much force does the road exert on the ball to bring it to rest?
(b) what is the direction of the force exerted by the road?
(c) define unit force.

Assume that the ball rolls to the right.

From the velocity-time graph, the acceleration is
a = (0 - 10 m/s)/(4 - 0 s) = -2.5 m/²

Part (a)
Because the mass of the ball is 25g or 0.025 kg, the force that the road exerts on the ball is
F = (0.025 kg)*(-2.5 m/s²) = -0.0625 N
The force is negative because it acts in opposition to the motion of the ball.

 0.0625 N to the left.

Part (b)
The direction of the force exerted by the road is to the left because it opposes the motion of the ball to the right.

Part (c)
The unit force is 1 N (Newton), with the dimension (kg-m)/s².