Question

An automobile travelling with a speed of 60 km/h, can apply brake to stop within a distance of 20m. If the car is going twice as fast i.e., 120 km/h, the stopping distance will be(a) 60 m (b) 40 m(c) 20 m (d) 80 m

Answer 1

The deceleration shall be the same.

Now, stopping distance should be given by:

S = v²/2a, where v is the speed the car is travelling with, and a the deceleration. (Using K1D)

So, the stopping distance is dependent on the square of the speed. Hence on doubling the speed, the stopping distance will quadruple (become 4 times).

So Sf = 4 * 20m = 80m (d).

Answer 2

This is the correct answer