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Peach
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Homework Statement
While doing a chin-up, a man lifts his body 0.40 m. The muscles involved in doing a chin-up can generate about 70 J of work per kilogram of muscle mass. If the man can just barely do a 0.40-m chin-up, what percentage of his body's mass do these muscles constitute? (For comparison, the total percentage of muscle in a typical 70-kg man with 14% body fat is about 43%.)
Homework Equations
W = F * s
The Attempt at a Solution
m = w/(g*s)
m = 70J/(9.8m/s^2 * .40m
m = 17.86 kg
Then I take this and divided by total mass 70kg to get the percentage but I got the wrong answer. I don't know why...what am I doing wrong here?
Homework Statement
Rotating Bar. A thin, uniform 12.0-kg bar that is 2.00 m long rotates uniformly about a pivot at one end, making 5.00 complete revolutions every 3.00 seconds. What is the kinetic energy of this bar?
Homework Equations
KE = 1/2m (vf^2 - vo^2)
The Attempt at a Solution
I didn't know how to get this started but I gave it a shot. First, I took the 5 revolution per 3 seconds and converted them to velocity.
5rev/3s (2*pie*r/rev) = 20.9 m/s
Then I take that answer and plug it into the kinetic equation but as expected, I was wrong. This kinetic stuff is really confusing or is it just me? Pls help?
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