Final answer:
The force to apply brakes on a subway car is provided by the braking system, which includes components like electric or pneumatic brakes or a spring bumper, converting the train's kinetic energy into another form.
Step-by-step explanation:
The force necessary to apply the brakes on a subway car is supplied by the braking system, which may include components like electric brakes, pneumatic brakes, or mechanical brakes such as a large spring bumper. In Physics, to calculate the force necessary to bring a subway train to a stop, one would apply the principles of Newton's laws of motion and energy conservation.
For example, if a subway train decelerates and comes to a stop, the change in its kinetic energy is absorbed by the braking system, converting the movement energy into another form, such as heat or potential energy in a spring. In a given scenario where a 5.00 x 10^5-kg subway train is stopped by a large spring bumper, the force constant k of the spring can be calculated using the work-energy principle where the work done by the spring equals the kinetic energy lost by the train.