Thursday, March 27, 2008

Random Physics

W = Fd

this is the formula for work.

Now for an example problem: A 50 kg runner runs up a tower 443m tall, in 15 minutes. What is his/her average power output in watts?

Anws - the runners total work is their weight multiplied by the height climbed. (mg)

W = mgh = (50kg)(9.80 m/s^2)(443m) = 2.17 x 10^5 J

since the time is 15 min = 900s, the average power is

2.17 x 10^5 J / 900s = 241W or .323 hp

Now for some practical application.

Lets say that there was a hot girl(50kg) being chased by a fat rapist(100kg). Should the hot girl run up a building(443m) or keep running on a flat surface(443m)? All other things constant the girl and the man both run at ave. 241 watts constant.

the girl running up the building:
W = mgh = (50kg)(9.80 m/s^2)(443m) = 2.17 x 10^5 J

2.17^5J/241w = 900s

the man running up the building:
W = mgh = (100kg)(9.80 m/s^2)(443m) = 4.34 x 10^5 J

4.34^5J/241W = 1800s

now on a flat surface

both the girl and the man put out the same 241 watts. The girl has no advantage

Lesson: When running away from a fat rapist run up hill he has to work harder against gravity ~9.80 to get to you.

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