Background: All Machines Are Typically Described by a Power Rating. the Power Rating Indicates

Name ______Per. _____

Power Lab

Background: All machines are typically described by a power rating. The power rating indicates the rate at which that machine can do work upon other objects. Thus, the power of a machine is the work/time ratio for that particular machine. To determine the power of a machine, one must be able to calculate the work done by the machine (through knowledge of the force it applies to displace an object) and the time it takes to do this amount of work.

A person is a machine which also has a power rating. Some people are more power-full than others; that is, they are capable of doing the same amount of work in less time. In this lab you will measure your own personal power by making measurements as you climb up a flight of stairs within your home.

Pre-Lab: In order to accomplish this lab, analyze the physical situation which you will be investigating and answer the following questions.

1. Construct a free-body diagram showing all the forces acting upon your body as you climb up one flight of stairs at a constant speed. Label the forces according to type.

2. Discuss how you will be able to measure the upward force applied to your body as you climb the stairs at a constant speed. (HINT: 1 kg of mass on Earth is equivalent to 2.2 pounds of weight.)

3. Write two equations - one for the work done upon your body as you climb the stairs and one for the power generated by your body.

4. Make a list of all the quantities which need to be measured in order to determine your personal power as you elevate your body up a flight of stairs.

Procedure: Once you have established a good understanding of the measurements which need to be made, set up a data table, make measurements, and proceed to calculate the power output of your body as you rapidly climb up a flight of stairs in your home. Use a ruler to determine the height of the stairs (Note: 12 in = 1 ft and 3.28 ft = 1.0 m). Use a stopwatch to determine the time.

Data and Calculations: Record all measured and known data below.

Calculate your power in the space below. PSYW

Post-Lab Questions: Express your understanding of the concept and mathematics of power by answering the following questions. PSYW.

1. A ski lift delivers two skiers to the top of a 500-meter tall hill every 12 s. The average mass of a skier plus equipment is 80 kg. Assuming dissipative forces are negligible; determine the power output of the chair lift motor.

2. A rock climber elevates her 55-kg body a height of 20 meters in 8 minutes. Determine her power output.

3. An elevator motor produces 2000 W. How fast (in m/s) can it lift a 1000-kg load?

4. A car must do work at a rate of 10 kW to maintain a constant speed of 25 m/s on flat ground. How large are the forces opposing its motion?

Conclusion: Write a conclusion which relates to the purpose of this lab.