A steam engine of 1kg pulls 8 cars of 1kg each. The velocity of the engine is 0m/s initially then gets up to 4m/s in a time of 4 s while moving a distance of 5.3 meters. During that time, the engine takes in 134J of heat. What is the change in internal energy? Ok so i know that: internal energy= Q + W and, W=Fd and, F=ma so, (8x1kg)(4m/s/4s) = 8 N = F also, W= (8N)(5.3m) = 42.4 so, internal energy = 134 J + (-42.4) = 91.6 However, the correct answer is about 62, what am i doing wrong?? It seems like the steps would make sense to get the correct answer.