Word Problem
A Formula One car is moving with a velocity of 162 km/hr. It takes 5 seconds to stop after the brakes are applied. Calculate the force exerted by the brakes on the car if its mass along with the driver is 900 kg.
Solution
The formula for force is given by F = m X a.
From the given problem, we know that m = 600 kg Now we have to calculate acceleration.
Acceleration is defined as the rate of change of velocity.
That is, a = v – u/t
 It is given that,
the initial velocity of the car, u = 162 km/hr,
the final velocity of the car, v = 0 km/hr (as the car comes to a halt) the time duration, t = 5 s
The SI unit of velocity = m/s.
So we need to convert the velocity from km/hr to m/s 1 km = 1000 m
1 hr = 3600 s
Therefore, u = 162 X 1000 m/s = 45 m/s
3600
v = 0 km/hr = 0 m/s
So, a = 0 – 45/5m/s = -9 m/s
Substituting the values of mass and acceleration in the formula for force, we get,
F = 900 kg X (-9)m/s
= – 8100 km m/s
= – 8100 N
The force exerted by the brakes on the car is – 8100 N.
 Here, the negative sign indicates that the force exerted by the brakes is opposite to the direction in which the car is moving.
If the car is moving towards the right, then the direction of the force of the brakes will be towards the left.