WEBVTT 00:00:00.000 --> 00:00:02.000 To figure out how many calories you burned, 00:00:02.000 --> 00:00:04.000 we're going to need to solve for how much work you do 00:00:04.000 --> 00:00:07.000 and we know from the work energy theorem that the work you do 00:00:07.000 --> 00:00:11.000 is equal to the change in energy of the weight.and the changed energy of the weight 00:00:11.000 --> 00:00:15.000 is equal to the change in it's kinetic energy plus the change in it's potential energy. 00:00:15.000 --> 00:00:22.000 Well the weight starts at rest and it ends at rest too, so the change in kinetic energy is zero. 00:00:22.000 --> 00:00:25.000 But it does change in potential energy when you raise it at 1 m. 00:00:25.000 --> 00:00:28.000 Okay, so using energy (mg)h for the potential energy of the weight 00:00:28.000 --> 00:00:33.000 and plugging in all my numbers, I do a little math and I get that each time I raise the weight, 00:00:33.000 --> 00:00:37.000 I need to do 100 joules of work but that's just for one raising of the weight. 00:00:37.000 --> 00:00:41.000 How much work do I have to do to raise it over my 4-minute workout. 00:00:41.000 --> 00:00:44.000 I chose to do this next part of the problem using conversion factors. 00:00:44.000 --> 00:00:48.000 The workout takes 4 minutes and there are 60 seconds in 1 minute, 00:00:48.000 --> 00:00:54.000 so these minutes are cancelled and we do 2/3 repetitions per second, 00:00:54.000 --> 00:01:01.000 so the seconds are cancelled, and we do 100 joules of work for each repetition, 00:01:01.000 --> 00:01:09.000 so repetitions are cancelled and there's 1 calorie per 4200 joules, so joules are cancelled. 00:01:09.000 --> 00:01:12.000 Okay, now let's multiply all these numbers together and we get that 00:01:12.000 --> 99:59:59.999 over the course of our 4-minute workout, we burned 7.62 calories. Great work.