Question

Two persons manage to push a motorcar of mass $1200\,Kg$ at a uniform velocity along a level road. The same motorcar can be pushed by three persons to produce an acceleration of $0.2\,m{s^{ - 2}}$. With what force does each person push the motorcar?
(Assume that all persons push the motorcar with the same muscular effort.)

Answer 1

Hint
Use the formula for Newton's second law of motion for calculating the force exerted on the car by the third person. Since the force provided by the third person alone constitutes for the acceleration of the car. The calculated force of the third person must be equal to the other two.
By the Newton’s second law of motion,
$\Rightarrow F = ma$
Where $F$ is the force exerted by the person on the car, $m$ is the mass of the car and then $a$ is the acceleration of the car.

Complete step by step answer
The given data are
Mass of the car, $m = 1200\,Kg$
Acceleration of the car, $a = 0.2\,m{s^{ - 2}}$

It is given that at first the car is managed to push by two members. After that the third person accompanied them to push the car for movement. Hence the force required for the acceleration of the car is provided by the third person only. The force of the third person alone is calculated by using the force formula.
$\Rightarrow F = ma$
$\Rightarrow F = 1200 \times 0.2$
$\therefore F = 240\,N$
Hence the force of the third person is $240\,N$. Since every adult person has the same muscular strength to each other, the force exerted by each person is $80\,N$.

Note
The first two person’s force helps to overcome the static frictional force and hence they two cannot make the car to move. When the third person accompanied them, his force along with the other two made the car move by accelerating it.