Question

Calculate the work required to be done to stop a car of 1500kg moving at a velocity of 10m/s.

Answer 1

Amount of energy in a moving body= 1/2mv².
Amount of energy in car =1/2 x 1500 x 10 x 10.
energy =150000 / 2
that is 75000 joules.

it means that if you want to stop the car.
you have to make its velocity 0.
after that the energy in the car will be zero.

what we are doing above is reducing its speed to 0.
in other words,
we are reducing its energy to zero.

suppose,
we are applying a force of 100 Newtons on that car.
then its velocity becomes zero after covering some distance.
distance will be given by the formula
Force X distance = work done
we have to work 75000 joules.
100 x distance = 75000 Joules.
distance = 750 metres.

from the above example.
we conclude that if we apply a lesser amount of force then the distance covered by car will increase.

as a result,
Force X distance will be constant.

so we have to work 75000 joules to make a car stop which is moving at a speed of 10 M / s.