2. On a train, a freight car of mass 20,000 kg moves along a frictionless level railroad track with a constant velocity of 15 m/s. When it comes to a stop in 3.0 seconds, what is the force required to stop the freight car?

Carbon is allowed to diffuse through a steel plate 15 mm thick. the concentrations of carbon at the two faces are 0.65 and 0.30 kg c/m^3 fe, which are maintained constant. if the preexponential and activation energy are 6.2 x 10-7 m2 /s and 80,000 j/mol, respectively, compute the temperature at which the diffusion flux is 1.43 x 10^-9 kg/m^2 -s.

By what factor does the drag force on a car increase as it goes from 65 to 110 km/h?

The gun from the crime scene shows tool marks where the serial numbers are ground off. there are also tool marks on the bullets left behind. what information can the tool marks on the bullets and gun provide about the crime? what type of evidence does this information provide, individual or class?