A Car of mass 1000kg applies a constant 200N breaking force over a distance of 30m and comes to a complete stop. How fast was the car going the instant the brakes were engaged.

Before we start we should have some idea of the route of our solution. We should observe that force, distance and work have a relation and that mass, velocity and work have a relation. So we should calculate the work done by the brakes stopping the car. W=FD so W = 20030=6000J We know work = change in energy and that the final energy is 0. So we now know that the starting energy of the car KE = 6000J We now look to the kinetic energy equation that states KE = 1/2 * m * v^2 solving for v we have v=sqrt(2KE/m) we now just plug in v = sqrt(26000/1000) = sqrt(12) = 3.46 ms^-1