physical science explorations
posted by Peter S. on .
A car of mass 900 kg moves at 10 m/s. What is the braking force required to stop the car in a time of 5 seconds?

The average veloicity during braking is 5m/s, so in five seconds, it goes 25m.
brakingforce*5m=1/2 900 10^2
solve for braking force. 
well if F=ma and a=vu/t (final velocityinitial velocity/time) so combining these two equations we get F=m(vu/t) which gives us F=mvmu/t
if the car is to stop then obviously the final velocity is zero (now this will give us a negative answer but that is OK because it is a retarding force)
so our equation is F = (09000)/5
which = 1800
so therefor that is 1800 Newtons of force required to stop the car from moving.
If you have any questions ask away because i know this can get a little confusing.