A car has a mass 1.2 ton what must be the force to stop the car when its velocity is 54 m/hr And time 5 sec.
Answers
We see that a force acts on the car, which was moving at a certain velocity, which leads the car to come at rest. That is to say the momentum of car changes. The force(F) acted on the car, m (1.2 ton), for some time, t (5 sec), to cause it to change its velocity from u (54m/hr) to v (0 m/hr), ie. its momentum changed from mv to mu by a force F which acted on the car for t seconds.
What is change in momentum?
It is called impulse.
I = Force x time for which force acts = change in momentum = mv - mu
F x t = mv - mu
F = (mv-mu)/t
Since, v =0, as the car stopped because of the force.
F = - mu/t
Negative sign means that, the force was applied in the direction opposite to that of the car's movement.
You can put in the values, take care of the unit conversion and get to the answer.
Just for your help. See how we do the conversion.
speed = distance(can be any unit)/ time(can be any unit)
In our case,
speed = 54 meters/ 1 hour
= 54 m / 60 minutes = 0.9 meters/ minute
= 54 m / (60 x 60) seconds = 54 m / 3600 sec = 0.015 m/sec