Lab 10: Work and Power
Joel Cook
Nina Song
Lab performed April 5, 2017
In this lab, we ventured outside perform experiments and calculate work and power done.
Introduction: Work done is calculated by finding the product of force on an object and displacement.
Introduction: Work done is calculated by finding the product of force on an object and displacement.
Power can then be found by calculating work per unit time. For the experiment, we performed work by pulling a mass up a rope and climbing stairs and measured the time for these tasks.
Procedure: For the first portion of the experiment, a known mass was tied to a rope and the rope run over a pulley braced against a balcony railing. The time to pull the mass to the heigh of the balcony was measured. the apparatus is pictured below.
For the second portion of the experiment, the height of one stair in a flight of stairs was measured and the total number counted to calculate the distance traveled. The time was measured to walk up the stairs and then the time was measured to run up the stairs. The flight of stairs is pictured below.
Work and power were calculated for each of the three events.
Data:
Pulling a mass:
A 5 kilogram mass was pulled a distance of 4.42 meters.
Work = force*displacement
w = m*g*h
w = 5 kg * 9.8 m/s^2 * 4.42 m = 216.6 joules
Power = work/time
P = 216.6 J / 6.34 seconds = 34.16 watts
Walking up stairs:
17cm/step * 26 steps = 4.42 meters
Time to walk up stairs = 12.48 seconds
w = m*g*h
w = 90.7 kg * 9.8 m/s^2 * 4.42 m = 3928.8 joules
P = w/t
P = 9328.8 joules / 12.48 seconds = 314.8 watts
Running up stairs:
Time to run up stairs = 7.98 seconds
P = w/t
P= 9328.8 joules / 7.98 seconds = 492.3 watts
Procedure: For the first portion of the experiment, a known mass was tied to a rope and the rope run over a pulley braced against a balcony railing. The time to pull the mass to the heigh of the balcony was measured. the apparatus is pictured below.
For the second portion of the experiment, the height of one stair in a flight of stairs was measured and the total number counted to calculate the distance traveled. The time was measured to walk up the stairs and then the time was measured to run up the stairs. The flight of stairs is pictured below.
Work and power were calculated for each of the three events.
Data:
Pulling a mass:
A 5 kilogram mass was pulled a distance of 4.42 meters.
Work = force*displacement
w = m*g*h
w = 5 kg * 9.8 m/s^2 * 4.42 m = 216.6 joules
Power = work/time
P = 216.6 J / 6.34 seconds = 34.16 watts
Walking up stairs:
17cm/step * 26 steps = 4.42 meters
Time to walk up stairs = 12.48 seconds
w = m*g*h
w = 90.7 kg * 9.8 m/s^2 * 4.42 m = 3928.8 joules
P = w/t
P = 9328.8 joules / 12.48 seconds = 314.8 watts
Running up stairs:
Time to run up stairs = 7.98 seconds
P = w/t
P= 9328.8 joules / 7.98 seconds = 492.3 watts
Conclusion/Questions:
a) Estimate kinetic energy neglected in calculating work done in experiment:
To estimate the kinetic energy in walking and running up the stairs, we first calculated the distance travelled up the stairs as shown below.
To estimate the kinetic energy in walking and running up the stairs, we first calculated the distance travelled up the stairs as shown below.
As shown, the kinetic energy was less than 1% of the work done so neglecting the kinetic energy in this experiment is appropriate.
b) How many flights of stairs would you have to climb to equal power output of a 1100 watt microwave?
As shown, I would have to travel 1.23 meters/second which translates to 7.24 stairs/second.
c) How many flights of steps total would you have to climb to be equivalent to the work to cook two potatoes in a microwave for 6 minutes?
The work to use the microwave for 6 minutes is 396000 joules. I would have to climb 100.8 flights of stairs at 4.42 meters/flight.
d) A person on a back can generate 100 watts continuously. A 100% efficient water heater requires 12.5 MJ for a 10-minute shower:
1) How much power is this?
2) How many people on bikes would be required to provide the power for the shower?
3) If instead you provide the energy yourself, how long would you have to ride the bicycle?
As shown above, the power for the 10-minute shower is 20833 watts. It would take 209 people on bicycle-powered generators to provide the energy. If I were going to supply the power myself, I would have to ride for 34.7 hours!
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