Question

A car (mass = 750 kg) is initially moving with velocity 30 m/s. The driver slowly presses on the brakes and bring the car to a stop, traveling 50 m in the process. Calculate the force of friction between the car and the ground that brings it to a stop. Draw a free-body diagram for the car and clearly explain the method behind your solution.
F * d = work done by friction = initial Ke = (1/2) m v^2

F * 50 = (1/2)(750)(900)
100 F = 750 * 900
F = 750 * 9

There are harder ways of course using
F = change of momentum/ time = 750*30/t
then
50 = (1/2)a t^2
where a = 30/t
so
100 = 30 t
t = 10/3 seconds to stop
a = 9 m/s^2 (about 1 g)
F = m a = 750* 9

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