1. The problem statement, all variables and given/known data A 1200kg car skids with uk = 0.45. If it skids 45.2m, find the thermal energy and the initial speed. m = 1200 kg Vi = ? Vf = 0 m/s (i think..because it wants to stop) uk = 0.45 (coefficient of friction) delta d = 45.2m 2. Relevant equations Well for Frictional force we use Ff = uk x Fn (0.45x11760) = 5292N 3. The attempt at a solution So I found the Fn which is 1200 x 9.8 = 11760 N Then I found Ff which is 0.45 x 11760 = 5292 N Then I found the work done (I don't know why thermal energy is the work can someone explain this please) W = F x d = 5292 x 45.2 = 239198.4 J But my textbook's answer key has a different answer for the thermal energy, it says it should be 5.3 kJ and 72km/h for the speed. How do we find the speed?