Question

A car travelling with a speed of 60 km/hr can brake to stop within a distance of 20m. If the car is going twice as fast, the stopping distance will be ?

Answer 1

u = 60 kmph = 60 x 5/18 m/s = 50/3 m/s and v = 0 m/s
stopping distance = 20 m
From the third equation of motion, $v^{2}-u^{2} = 2as$
0 - 2500/9 = 2a(20)
a = - 125/18 m/s^2

Now, u = 100/3 and v = 0
We have a = -125/18 m/s^2
So, 0 = 10000/9 = 2 (-125/18)s
Implies s = 10000/125 = 80 meters