Question

A car travelling at a speed of 30 km/h is brought to a halt in 8 meters by applying brakes. If the same car is travelling at 60 km/h it can be brought to a halt with the same breaking power in 

(A) 8 m 

(B) 16 m 

(C) 24 m 

(D) 32 m

Answer 1

Correct option: (D) 32 m

Explanation:

car is brought to halt i.e. final velocity = o.

V = V_o + at

V_o = – at

Also,

S = V_ot + (1 / 2) at² 

S = (– at) t + (1 / 2) at² 

S = – (1 / 2) at² 

i.e. s × t² 

(s₁ / s₂) = (t₁ / t₂)² 

as V_o = – at means t = (– V_o / a)

(S₁ / S₂) = [{– (V_(o)1 / a)²} / {– (V_(o)2 / a)²}]

(S₁ / S₂) = {(V_(o)1) / (V_(o)2)}² 

(8 / S₂) = {30 / 60}² 

S₂ = 8 × 4 = 32 m