### All AP Physics B Resources

## Example Questions

### Example Question #13 : Work, Energy, And Power

A crane lifts a steel beam to a height of . If the task is accomplished in , what was the average power provided by the crane?

**Possible Answers:**

**Correct answer:**

To find average power, we find the total work done by the crane in lifting the steel beam, and then divide it by the time taken to complete the task.

In this case, the total work done is equal to the change in potential energy of the steel beam. for this, we use the potential energy equation:

We then divide the work by to find average power:

### Example Question #5 : Power

A crane is being used to lift a crate to a height of above the ground. If the crane's engine can provide a power output of , how long does it take for the crane to complete the task?

**Possible Answers:**

**Correct answer:**

First we find the total work required to lift the crate:

We are given the mass, change in height, and the acceleration of gravity. Using these values, we can solve for the total work done.

Next, we can use the equation for power to find the time to complete this task if the engine is working at its maximum power.