Question

24. A car is travelling along an expressway at 90 km/h. The driver spots a stalled car and some traffic congestion on the road ahead, and so applies the brakes. The braking action causes a frictional force of 8400 N to act on the 1050 kg car. (a) What is the acceleration of the car when the brakes are applied? (b) How long does it take for the car to stop? (c) How far does the car travel while it is braking?

Answer 1

Answer:

See explanation

Explanation:

We convert the speed of the car to ms-1

90 × 1000/3600 = 25 ms-1

a) from;

F= ma

a= F/m

a= 8400/1050 = 8 ms-2

b) from

v= u - at

v= 0

u = 25 ms-1

a= 8 ms-2

t= ?

t = u/a = 25/8 = 3.1 s

From;

v^2 = u^2 - 2as

v= 0 ms-1

u^2 = 2as

s = u^2/2a

s= (25)^2/2 × 8

s= 625/16

s = 39 m