00:01
So here, the 4 -part a, the rate of change of the gravitational potential energy, we can say that the derivative of the gravitational potential energy with respect to time would be equal to m -g times the change in the height or change in the y position with respect to time.
00:21
And this is simply going to be equal to negative m -g times the absolute value of the velocity.
00:27
This is simply due to the definition of velocity.
00:30
So we can say that the change in the gravitational potential energy with respect to time, which would be the derivative essentially, this would be negative 68 kilograms multiplied by 9 .8 meters per second squared, multiplied by 59 meters per second, and we can say that this is equaling negative 3 .9 times 10 to the 4 joules per second.
00:57
This is not conventionally a power, so we're not going to say watts.
01:02
We're just going to say joules per second.
01:05
We could say watts, but again, it's, we could say watts, but again, it's just joules per second because we are trying to find the change in potential energy with respect to time.
01:15
So according to the definition of these units, it is a bit better to write it in terms of joules per second...