A driver is driving a car with a velocity of 54 km/h, and it takes 2 s to stop after the brakes
are applied. Calculate the force exerted by the brakes on the motorcar if its mass along with
the driver is 900 kg.
Answers
Given info : A driver is driving a car with a velocity of 54 km/h and it takes 2 sec to stop after brakes applied.
To find : the force exerted by the brakes on the motorcar if its mass along with the driver is 900 kg, is ...
solution : initial velocity of the car, u = 54 km/h = 54 × 1000m/(60 × 60s)
= 54 × 5/18 m/s = 15 m/s
time taken to stop the car, t = 2 sec
final velocity of the car, v = 0 m/s [ ∵ finally car has been stopped ]
now using formula, v = u + at
⇒ 0 = 15 m/s + a × 2m/s
⇒ a = -7.5 m/s²
negative sign indicates that retardation of car.
now force exerted by the brakes on the motorcar, F = m|a|
= 900 kg × 7.5 m/s² = 6750 N
therefore the force exerted by the brakes on the motorcar is 6750N.