Question

A car moving along a straight highway with a speed of 126 km h^-1 is brought to a stop within a distance of 200 m. What is the retardation of the car (assumed uniform), and how long does it take for the car to stop?

Answer 1

 v₀ = 126 kmh^-1

= 126 × (5/18)ms^-1 = 35 ms^-1

Stopping distance = (x – x₀) = 200 m

Since the car is stopped, v = 0.

v₂ = v₀² + 2a(x – x₀)

0 = 35² + 2a(200)

⇒ a = – 3.06 ms^-2

Retardation = 3.06 ms^-2

v = v₀ + at

⇒ 0 = 35 – 3.06 t

⇒ t = 11.4 s

Time for car to stop = 11.4 s.