Hi guys, I know that the simple definition of work done is just Work=Force X Displacement. If this is the case, there are 2 scenarios which I dont really understand. 1. If say the force applied on a car moving at constant velocity at 5m/s is 500N for a distance of 10m (therefore 2 sec), and the friction work done on the car which is also 500N- hence the constant velocity,the work done on the car by definition is 5000J. What happens to the 5000J of energy if the car does not gain it in KE (velocity is constant)? If say another car was acted on by the same forces and same amount of time but was not moving at all- started at 0 velocity did not accelerate due to friction, then by definition no work is done on the car as there was no displacement. I can't get how this could be possible. In both cases you must have used the same effort. Can someone explain this to me please? 2. If the heat of reaction of a chemical reaction forming an expandable gas is measured in a system of which you forced to have constant volume, then does the mechanical work done- expansion of the gas, get converted into heat energy?(therefore increase of temp) if it does not, what happens to the mechanical energy? Thank you very much again for answering my newbie questions.