Question

a car, running at a speed of 72km/h is slowed down to 18km/h over a distance of 40m. calculate the retardation produced by its brakes, and time for which brakes are applied​

Answer 1

Explanation:

u = 72 kmph or 20 m/s

v = 18 kmph. or 5 m/s

s = 40 m

using 3rd equation of motion v² = u² + 2as

5² = 20² + 2×40×a

25 = 400 + 80a

80a = 25-400

a = -375/80

a = - 4.687 m/s²

Hence retardation is - 4.687 m/s²

v = u + at

t = v-u/a

= 5-20/-4.687

= -15/-4.687

= 3.2 second