Question

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

Answer 1

Initial velocity,

u = 126kmh^-1 = 126 × \(\frac{5}{18}\) ms^-1 = 35m^-1

Final velocity, ν = 0;

Distance, S = 200m

Using ν² – u² = 2aS,

0² – 35 × 35 = 2a × 200

or

a = −\(\frac{35×35}{400}\) ms^-2

= 3.06 ms^-2

So, the retardation of the car is 3.06 ms^-2

Using ν = u + at,

0 = 35 - 3.06 × t

or

3.06 t = 35

t = \(\frac{35}{3.06}\)s = 11.4s.