Question

A bus is travelling at 55.0 km/hr. After it has travelled 95 m the brakes are applied giving a constant deceleration of -5.7 m/s2. How far from the starting point does it stop?

Answer 1

let us assume a point A from where bus is travelling with velocity 55 km/h.

assume a point B where still it is travelling with velocity 55 km/h , whuch has covered a distance of 95m and this is the point at which now a constant retardation (deaceleration) is to be applied.

finally the bus comes to rest at a point C where velocity becomes 0 km/h.

now we have to find out the total distance covered between A and C.

distance covered between A and B is given to be 95 m.

now between B and C.

initial velocity, u = v_B = v_A = 55 km/h = 55 * 5/18 m/s

& final velocity , v = v_c = 0 m/s

so by applying newton's formula

v² - u² = 2as

we get, (0)² - (u)² = 2 * (-5.7) * s

- (55*5/18)² = - 2 * 5.7 * s

on solving we get

s = 20.2 m

so total distance covered = 95 + 20.2 = 115.2 m