I get most of the things in my text book, such as mgh,Fs and 1/2mv squared. But I don't understand things about stopping force and stuff. heres a practice question i got(i have a test 2morrow): A boy of mass 50 kg rides on a bicycle of mass 15 kg at a speed of 15 m/s. He suddenly applies the braked and brings the bicycle to a stop in 25m. What force did the brakes apply to the wheels as he was stopping? I really don't understand how to do this... please help!!!