A driver stops his car in time t by gradually increasing the total braking force on the car.

Question 23

A driver stops his car in time t by gradually increasing the total braking force on the car. The graph shows the resultant force on the car.

 

Which graph shows how the speed of the car will vary during this time?

Reference: Past Exam Paper – June 2017 Paper 13 Q7

Solution:

Answer: D.

The total braking force on the car increases with time.

F = ma

So, the deceleration of the car increases with time. This means that the speed decreases at an increasing rate.

From a speed-time graph, the deceleration can be obtained by the gradient. Deceleration is indicated by a negative gradient.

I

n this case, the gradient is negative and increases with time.

D is the only graph where the gradient keeps on increasing with time.