How powerful are freight train car air breaks?

If a coal car is loaded to maximum capacity (100 tons) and traveling at 60k/h on a level grade, how many meters does it take the car to come to a stop when the emergency air break of the coal car is activated?

If you have no idea I'm basically just trying to figure out how much stopping power the air brake

If a coal car is loaded to maximum capacity (100 tons) and traveling at 60k/h on a level grade, how many meters does it take the car to come to a stop when the emergency air break of the coal car is activated?

If you have no idea I'm basically just trying to figure out how much stopping power the air brake (by itself) has on a normal freight car. If you have any insight, or know where I can find the answer, please tell me. I've been researching this for 2 days now and I've just been hitting one dead end after another.

Other answer:

Dylan:
The car by itself would stop on a level surface within fifty feet but when the cars are uncooked or not coupled the brakes are activated. Did you know the average man can push an empty railroad car on a flat surface do to the efficiency of the running gear?
Rona Lachat:
I'm basically just trying to figure out how much stopping power the air brake (by itself) has on a normal freight car.

Fascinating question. Just curious WHY do you need to know the stopping distance of a coal car in EMERGENCY brake.

The major factor of stopping distance is the speed it is going when the brakes are applied.

The grade is rarely perfectly level. New brakes old brakes.

http://www.minnesotasafetycouncil.org/fa…

Buy the book if you really want to know.
http://www.train-dynamics.com/

The Chiel:
It is something that can be figured out to a reasonable accuracy with a little applied maths – I am afraid that mine's got rather rusty the years. However, we know the weight of the car – load plus empty weight, and dividing this figure by 8 gives us the weight on each wheel (assuming two four-wheeled bogies or trucks). From the co-efficient of friction between steel tyres and steel rails, the 'limit of adhesion' between them can be found, given the fact that the contact area between them is about 1cm^2, and the force between them is as calculated above. Thus, we now know the maximum retarding force acting against the motion of the loaded car moving at 60 km/h and can calculate the retardation rate, and hence the total stopping distance.
Harry:
the brake pads are far more efficient than rail traction. more than adequate to lock the wheels, but an object in motion tends to stay in motion even when the wheels are locked up