May Soe Moe
Lab partners: Ben Chen, Steven Castro
5-April-2017
Objective: To calculate the work and power output produced during performance of activities such as walking up the stairs, running up the stairs, and lifting up a bag of certain mass to a height h that is connected to a rope and a pulley.
Introduction: In our daily lives, we do work and produce power, which in Physics work equals force applied and distance traveled, and power is work divided by time. We can also relate to power in our daily lives, especially as the technology improves nowadays. We use power to produce electricity, to light up our homes, to watch TV, to charge our mobile phones and laptops, and to heat up our food in microwave. We have to use power even to use internet. But we have no idea how much it takes to produce power. Therefore, we tried to do work by walking up the stairs, running up the stairs, and lifting up a bag with mass to a height, which was attached with a rope and a pulley. Using our known formulas of work and power, we would calculate the work done and power output during the activities. Using the same formulas, we could calculate how much it takes to produce power for our everyday activities as mentioned above. In this case, our work done and power output were:
Part 1:
(1) The professor set up the rope that goes over pulley. At the end of the rope from the ground, three backpacks with different masses (5 kg, 6 kg, and 9 kg) were tied. At the balcony, the pulley was tied to a wooden stick so that it could be used to connect to the rope and the backpack.
(2) During this procedure, we were to lift up a backpack containing a known mass (5 kg, 6 kg, and 9 kg) from the ground to the wooden stick by pulling on the rope that went over a pulley-- tied to a wooden stick at the balcony.
(3) Each individual in the group was to complete the experiment and to get timed for their own since individuals' time to complete the experiment were different depending on the ability and strength to lift the backpack. We could also choose which backpack we wanted to lift up. When pulling up the backpack, one person from the group had to press down the wooden stick that was tied to the pulley so that it would not move up and hurt the people passing by.
(4) My time to lift up the backpack was 49.93 seconds, the backpack I lifted up contained 5 kg, and the height from the ground to the balcony was 4.5 meters.
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| Lifting up the backpack |
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| Walking up to the stairs |
Calculation For Part 1:
The power output to lift up a 5 kg backpack for me came out to be 4.42 Watts.
Part 2:
(1) For this part, each individual from the group walked up the stairs and got timed to get to the top of the stairs.
(2) We measured the height of a step of a stair, which was 17 cm or 0.17 m. There were 26 stairs, therefore, the total height was 26 stairs x 0.17m, which came out to be 4.42m.
(3) My power output to reach the top of the stairs came out to be 223.1 Watts.
Part 3:
(1) We timed while running up to the stairs. The height of the stairs was the same from part 2. Calculation of my power output to reach the top of the stairs was 441.7 Watts.
Conclusion:
(4a) Q: In our analysis, we neglected our kinetic energy in calculating the total work that we did. Make a reasonable estimate of how big of an error this introduces into your results.
Calculation:
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| Calculating the distance L of a flight of stairs |
My calculations tell me that error of kinetic energy for lifting up the 5 kg backpack was 0.009%, error of kinetic energy for walking up the stairs was 0.6%, and the error of kinetic energy for running up the stairs was 2.4%. All the errors were under 5%, which is in acceptable range, therefore, the negligence of kinetic energy in calculating my total work that I did was not affected.
(4b) Q: A microwave oven typically has a power consumption of approximately 1100 Watts. How many of the flights of stair we used in this lab would you have to climb each second to equal the power output a microwave oven?
Calculation:
(4c) Q: Suppose you are cooking two potatoes in the microwave oven for a total of 6 minutes. How may flights of steps total would you have to climb to be equivalent to the amount of work that it took to run the microwave?
Calculation:
(4d) A person in reasonably good shape can comfortably put out 100 Watts continuously (say, by riding a stationary bicycle connected to a generator.) A 100 % efficient water heater would require about 12.5 MJ (megajoules - 10^6 joules) of energy to heat water for a 10-minute shower (flow rate of 10 liters per minute, approximately 2.5 gallons per minuter, water being heated from 20 Degrees Celsius to 50 Degrees Celsius.)
(Q1): How much power is this?
Calculation: Power to heat water came out to be 20833 Watts.
(Q2): If you gathered a group of people to ride bicycle-powered generators in order to heat the water for your shower in real time, and each one was putting out 100 Watts, how many people would it require to heat the water for your shower?
Calculation: 208 men are needed to heat the water for my shower.
(Q3): If instead you were going to provide all of the energy yourself, how long would you have to ride on a bicycle-powered generator in order to heat water for your 10-minute shower?
Calculation: I need to ride a bicycle-powered generator for 124998 seconds if in seconds, 2083 minutes if in minutes, or 35 hours if in hours in order to heat water for my 10-minute shower.
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