Question

A car is moving in a circular motion on a road with friction coefficient $\mu$. It starts slipping when its speed is increased. This is because:
(a) The tyres start burning
(b) The force of friction is not sufficient
(c) The mass of the car decreases
(d) None of these

Answer 1

In order to understand the correct answer, we have to have a good concept of centripetal force.
As stated in the question that the car is in circular motion on a road which has friction coefficient $\mu$. It starts slipping when the speed is increased. This is because when a car moves in a circular motion on a road, the force of friction provides the necessary centripetal force. When the car's speed increases, the centripetal force required to maintain the motion becomes greater than the friction force and so the car starts slipping.

Therefore, the correct answer for this question is option (b).

Additional Information: Any net force causing uniform circular motion is called a centripetal force. The direction of a centripetal force is toward the center of curvature, the same as the direction of centripetal acceleration. According to Newton’s second law of motion, net force is mass times acceleration: net$F\text{ }=~ma$. For uniform circular motion, the acceleration is the centripetal acceleration$a~=~ac$. Thus, the magnitude of centripetal force ${{F}_{c}}$ is ${{F}_{c}}~=~m{{a}_{c}}.$

Note: While solving this question, we need to have a good concept about centripetal force, how and why centripetal force is important.The direction of the net force is in the same direction as the acceleration. So for an object moving in a circle, there must be an inward force acting upon it in order to cause its inward acceleration. This is sometimes referred to as the centripetal force requirement.