Question

A car of mass 800 kg, moving at 54 kmh⁻¹ is brought to rest over a distance of 15 m. Find the retarding force developed by the brakes of the car.

Answer 1

Mass of car = m = 800 kg
Initial velocity of car = u – 54 kmh⁻¹

u = `54xx5/18` ms⁻¹ = 15 ms⁻¹
Final velocity of car = v = 0
Distance covered = S = 15 m
Retarding force = F = ?
v² – w² = 2a S
(0)² − (15)² = 2a(15)
30 a = −225

a = `-225/30`
a = −7.5 ms⁻²
F = ma = (800) (−7.5)
F = −6000N