posted by Lindsay .
A railroad flatcar is loaded with crates. The coefficient of static friction between the crates and the floor is 0.27. If the train is moving at 59.7 km/hr, in how short a distance can the train be stopped with a constant acceleration without causing the crates to slide?
Ok so I understand that mu*mass*g = mass*v^2/2d, and I need to solve for d. But how do I get the mass?