In: Physics
A. Net force = mass * acceleration = 1250*20 = 25000 N or 25 KN
B. When the breaks are hit a pressure chamber releases the break fluid. The pressure fluid on reaching the break pads make it touch the revolving rotor. The friction force between the break pad and the rotor slows down the rotor and causes the de deceleration.
C. Force on driver = 60*20 = 1200 N or 1.2 KN.
D. The cause of the driver's deceleration is the same as the driver is in the inertial frame of the car. But when the brake is applied suddently there is not enough time to stop the motion of drivers and hence the driver feels a forward force. This is the reason seat belts are necessary.