For a project i had to make a propeller that pushes along a small trolley at different voltages. I made the propeller and buggy, and i lay them on a wooden track. Using the time taken to accelerate accross the 30cm track, i was able to find the acceleration, and hence the force that the propeller produces at that voltage. Of course, to this i can add friction which is the weight of the trolley x Mu so as to find the total force that the propeller produces. I also have to find the efficiency of the propeller. Now i know the Energy produced by the powerpack is V x A x t. But i am not sure how to find out how much energy was gained by the trolley during the time it took to cross the track. Can anyone help (bear in mind it is not travelling at a constant speed). Thanks.