April 03, 2017 Lab 10: Work and Power

Lab 10: Work and Power

Chris Ceron, Amy Chung, John Choi

Goal of Lab

Perform various physical activities and record force, distance, and time for power

Theory/Introduction

Work in relation to force is:

F = Force

 = change in displacement 

Power is the relationship between how much work is done in relation to time:

Experimental Procedure

We did three activities to find our power output.

1) Lift a known mass up by a measured distance

We used a pulley system to pull a backpack with a known mass up to the second floor balcony

Through a free body diagram, we were able to find an equation for the Force we used to pull the backpack up:

To find work, we multiply this force by  (the displacement of the backpack from the ground to the balcony)

We used this to find power

2) Walk up stairs and record the time taken to complete

3) Run up stairs and record the time taken to complete

These two activities are almost identical, except one involves walking and the other running. Through a free body diagram, we found that:

Similar to activity one, we found the work output by multiplying force times displacement

We used this to find power

Data:

time 1 (sec)	time 2 (sec)	time 3 (sec)
4.65	15.8	8.5

The height of one stair was 0.169 meters. There were 26 stairs, so the total height = 4.394 m.

mass of the backpack in activity one = 5kg

my mass for activity two and three = 86.2 kg

Power 1 (Watts)	Power 2 (Watts)	Power 3 (Watts)
46.3	234.9	436.7

Conclusion:

a) There would be some measure of kinetic energy. Assuming my final velocity was 1 m/s, my final kinetic energy would be:

My work from gravitational potential energy was:

The ratio from KE to GPE is 43.1/3711.9 which is .0116 or 1.2%. The amount of error is relavtivately small, but show how some quantities are ignored.

b) Assuming one flight of stairs is equal to the 26 stairs, I generated 436.7W running up one flight of stairs. 1100 Watts / 436.7 Watts gives us a ratio of 2.5. I would need to climb 2.5 flights of stairs to equal the power output of the microwave oven.

c)The power output of the microwave is 1100W per second. To get the total power output, you multiply this by 6 minutes of 360 seconds. That equals to 396000 Joules. The work done climbing one flights of stairs was 3711.9, so 396000/3711.9 equal to 106.7 flights of stairs.

d) 1) Power = Work/Time. So 12.5MJ/10 minutes or 600 seconds = 20833.3W

2) 20833.3W divided by 100W per person = 208.3 persons.

3) If you were the only person providing energy and you put in 100W, you would have to ride 208.3 seconds to hear water for your 10-minute shower.

The lab ignored several factors that would alter the results obtained. For example. we did not take into account the kinetic energy obtained from running up the stairs. In activity one, the force was exerted on the bag was not constant, and friction between our hands and the rope was ignored. This is a large uncertainty as there was little grip and a lot of friction between our hands and the rope. For this lab however, these factors were ignored to simply calculate a power output.