In the following cases,identify the direction of the net force acting on the objects:
$(a)$ $A$ car drives around a circular race track at a constant speed.
$(b)$ Earth moving around the sun.
$(c)$ $A$ ball,rolling across a grassy field,slowly comes to a stop.

(N/A) The car is performing uniform circular motion. The net force acting on it is the centripetal force,which is directed towards the centre of the circular track.
$(b)$ The Earth is revolving around the sun in a nearly circular orbit. The net force acting on the Earth is the gravitational force exerted by the sun,which is directed towards the sun.
$(c)$ The ball is moving on a grassy field. The net force acting on it is the frictional force,which acts in the direction opposite to the direction of motion,causing the ball to decelerate and eventually come to a stop.