Question

A motor car is running at the rate of 7m/s can be stopped by applying brakes in 10m. show that total resistance to the motion of car, when brakes are on its one fourth of the weight of car?

Answer 1

Using v² = u² + 2aS,

Here: v = 0 (stoppage)

u = 7 m/s

a = ?

S = 10m

So, 0 = 49 + 2a(10)

Or, a = -49/20 m/s² = -2.45 m/s²

Since the retardation is 2.45m/s², using F = ma, the resistance due to braking shall be F(r) = m(2.45), where m is the mass of the car.

The weight of the car is given by mg = m(9.8), where m is the mass of the car.

So, evidently, the weight is 4 times the resistive force offered by braking.

Answer 2

Here's your answer. Hope it's helpful