This can be a tricky question. You need to rely on the work-energy theorem, which states:

Since the elevator is at rest at both the beginning and end, the net work is 0; there is no net change in energy, and therefore no work.

This theorem can be confusing to some since it completely negates potential energy. However, let's think about the situation presented in the problem. A force is required to raise the elevator, meaning that energy is put into the system. However, since it comes back to rest, all of the energy that was put in has been removed by the force of gravity, resulting in a net of zero work.

Since the truck is traveling at a constant rate, we know that all of the power exerted by the truck is going into a gain in potential energy. The power exerted will be a function of the change in potential energy over time. Therefore, we can write the following formula:

is a vertical height, so we need to write that as a function of distance traveled up the slope:

We can substitute velocity into this equation:

We have values for all of these variables, allowing us to solve:

Because all of the force was in the Y direction, all of the work will come from the change in the Y coordinate.

We will use the definition of work

First we need to find the distance traveled.

Then we can plug that into our work equation.

Work is a measure of force and displacement . Because C.J. did not move the phone at all, no work was done.

This can be a tricky question. You need to rely on the work-energy theorem, which states:

Since the elevator is at rest at both the beginning and end, the net work is 0; there is no net change in energy, and therefore no work.

This theorem can be confusing to some since it completely negates potential energy. However, let's think about the situation presented in the problem. A force is required to raise the elevator, meaning that energy is put into the system. However, since it comes back to rest, all of the energy that was put in has been removed by the force of gravity, resulting in a net of zero work.

We can assume that the dog must carry his entire weight up the tree, and therefore a force is exerted. Using the equation

we can use the evidence provided by the problem to solve for distance.

Initially the car is at rest at the bottom of a hill, this velocity and height are zero.

Converting to

Plugging in values:

Work is found by finding the change in kinetic energy. Since the car started from rest it had no initial kinetic energy.

Divide by 1000 to convert to kilojoules and get 5400 kilojoules.

Based on the information given, his throw would have started at above the ground. The pizza gained a maximum height of . Thus, the gravitational potential energy in relation to the starting position will be:

Since at it's maximum height, all of the energy will be gravitational, the work done on the pizza will be equal to the potential energy, thus:

Using