Question

The car has a total mass of 900 kg and is travelling at 20 m / s. At time t=0, the driver sees an
accident ahead. He applies the brakes at t = 0.60 s to stop the car. After the brakes are applied,
the car comes to rest in a further 4.0 s.
(i) Calculate the deceleration of the car as it brakes.

Answer 1

Answer:

initial momentum = 900 × 20 = 18000

final momentum = 0 ( as the car stops )

change in momentum = 18000 - 0 = 18000

time taken for this change = 4 - 0.6 = 3.4 sec

now we know : force = change in momentum / time

therefore force on the car due to brakes will be :

F = 18000 / 3.4

hence deceleration will be

ma = - 18000 / 3.4

a = - 18000 / 3.4 × 900

a = - 5.9 m/ sec^2