Lab Questions on gravitational potential energy and Kinetic Energy

[NeomiXD]

In this investigation I had to calculate my maximum power as I run up a flight of stairs. These are a few questions that I have for my lab. I want to know if my calculations are right.

Given:

1. mass: 70kg
2. h = 1.17m
3. d= 1.78m
4. t = 2.02s

Use the information from 1 and 2 to find the change in gravitational potential energy.

ΔEG = mgΔh
ΔEG = (70kg) (9.8 N/kg) (1.17m)
ΔEG = 802.62 J


Use the information in steps 1 and 3 to find average kinetic energy.

v = Δd/Δt
v = 1.78m/2.02s
v = 0.88m/s

Ek = mv²/2
Ek = (70kg) (0.88m/s)²/2
Ek = 27.10 J


Using the information in steps 4 and 7 find your power.

W = (27.10J) (1.78m)
W = 23.08 W

P = W/Δt
P = 48.24 J/2.02s
P = 23.88 W

 

[amy andrews]

Gravitational energy looks fine. I'm pretty sure your kinetic calculation is all right too, unless they want you to find the total distance traveled (using the height and the horizontal distance). There seems to be some confusion in the third part. Remember Work=FORCE*distance, not energy*distance, and remember the units of force and work are Newtons and joules (units of energy are the same as for work).

 

[NeomiXD]

Is this right for the third part

P = Ek/Δt
P = 27.10 J / 2.02s
P = 13.42 W

 

[amy andrews]

Well...this is what I think. Remember that the full equation for work is F*d cos theta. If theta is 90 degrees (the force is perpendicular to the distance) cos theta is 0. So, I think you shouldn't use the kinetic energy for this, it is changing perpendicular to the distance you are looking at (the height). Use the change in gravitational energy for this, and you'll be done.

 

[rwisz]

Your calculations appear to be correct. However, it is always a good idea to double check your work and make sure all units are consistent. Also, consider discussing any potential sources of error in your measurements or calculations. Overall, your results show that you have a power output of 23.88 watts while running up the stairs, which is a good indicator of your physical fitness and strength. Keep up the good work!