There will be no work done.

Energy is a scalar quantity. Since it has the same amount of energy in the end as the beginning, no work was done.

Alternatively, it can be modeled as the floor did negative work during the first half of the bounce (when the ball was compressing), and did positive work of the same magnitude and opposite sign in the second half of the bounce. This is due to the direction of the ball's motion flipping and the Force vector of the floor staying the same.

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

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

Converting  to 

Plugging in values:

The equation for work is:

Where  is the work done on an object,  is the force applied to an object,  is the distance the object moves, and  is the angle between the applied force and the direction the object moves.

From the problem statement we have:

 but .

Plugging in to our equation we find:

Because the rock does not move, no work is done on the rock. 

Note: the unit for work is shown to be  and a Newton-meter is the same as a Joule so  would also be an appropriate answer.

The equation for work is:

Where  is the work done on an object,  is the force applied to an object,  is the distance the object moves, and  is the angle between the applied force and the direction the object moves.

From the problem statement we have:

 and .

Plugging in to our equation we find:

We can assume that the bulldozer is pushing straight in to the rock because no information is given about the angle between the force and distance, so we can assume that  and  and that part of the formula can be ignored in this problem.

The time it takes to move the rock is superfluous information as work does not have a time component.

Note: the unit for work is shown to be  and a Newton-meter is the same as a Joule so  would also be an appropriate answer.

This question asks you how to calculate the work done by gravity on a block that is dropped from the air. Work is calculated by multiplying a given force by the distance over which the force acts. In this case, you are asked to find the work done strictly by the force of gravity on the block. The force of gravity works over the distance from which the block is dropped, to the ground (i.e. the height of the block, ). Thus, you can set up the equation as follows:

Therefore, the work done by gravity on the block is 

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.

Think about this scenario practically. After the jumper jumps, he will begin accelerating at a rate of . This rate will stay constant until the bungie cord begins to stretch. At this point, the jumper has traveled a distance of . The rate of acceleration will now decrease and ultimately reach a rate of . This is the point at which the force from the bungie cord is equal and opposite to the force of gravity. This is also the point at which the jumper is traveling at his or her maxmium velocity. With all of this in mind, let's start writing expressions for the scenario.

The main expression we will use will be the one for conservation of energy:

Plugging in our expressions for these variables and removing initial kinetic energy, we get:

Rearranging for velocity:

We simply need to find the height distance between the jumper's initial position and the position at which the jumper is traveling at his or her greatest velocity. As previously mentioned, the point of highest velocity is the point at which the force from the bungie cord is equal and opposite to the force of gravity:

Rearranging for , we get:

This is the distance that the bungie is stretched. Therefore, we can say that the total height distance between the initial and final state is the length of the unstretched bungie cord plus the distance the cord has stretched:

Plugging this back into the equation for final velocity, we get:

We have values for all of our variables, so we can simply solve for the final velocity: