Question

A uniform car of mass 500g travels with a uniform velocity of 25 ms^-1 for 5 s. The brakes are then applied and the car is uniformly retarded and comes to rest in further 10 s calculate 

1) the retardation

2) the distance which the car travels after the brakes are applied 

3) The force exerted by the brakes.

Answer 1

Mass of toy car = 500 g = 0.5 kg

Initial velocity, u = 25m/s

Final velocity, v = 0 m/s

From equation v = u + at

0 = 25 + a x 10

Acceleration , a = -2.5 ms^-2

1) Retardation = - acceleration = 2.5 ms^-2

2) From equation : `v^2 - u^2 = 2 as`

`0^2 - (25)^2 = 2 xx (-2.5) xx s`

-625 = -5s

S = 625/5 = 125 m

3) Force exerted by brake, F = ma

F = 0.5 x (-2.5)

= -1.25 N

Resistive force exerted by brakes = 1.25 N