Calculating the Tumble Buggy horsepower. These cars are very popular in the physical science classroom, they are cheap, sold by several outlets and hold up fairly well with a bit of care. As part of our study of energy and power studies, I had my middle school students see if they could calculate the car motor's power and horsepower using one method and then compare it to another method. The first method, work divided by time and the second, voltage times the amperage both yielded the same unit of watts but were vastly different in their values. Obviously we can't take the motors out of the cars and there are several variables that can affect our results, but I would be very interested in hearing what's right or wrong in this lab assignment. Keep in mind that this is a middle school activity for 7th and 8th graders.