Question: A weight lifter pushes dumbbells of total mass 20 kg upward with a force of just a little more than the weight of the dumbbells a distance of 1.2 meters. He then lets the dumbbells drop back down without doing any work on them.
Part A: If he wants to use (actually: convert) 50 kCal of energy in this workout, how many repetitions does he have to do? (There are 4.2 Joules in a calorie and 1000 calories in a kCal).
Please, show work so I can understand the concept. Thanks.