Homework Help: Circular Motion -- maximum speed Tarzan can tolerate at the lowest point of his swing?

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1. Nov 11, 2014

Quantum Fizzics

1. The problem statement, all variables and given/known data
Tarzan plans to cross a gorge by swinging in an arc from a hanging vine. If his arms are capable of exerting a force of 1500N on the rope, what is the maximum speed he can tolerate at the lowest point of his swing? His mass is 85kg; the vine is 4.0m long

2. Relevant equations
Fc = mv2/r
Fg = mg
T = Fc +Fg
Fc = T-Fg
3. The attempt at a solution
How I did it at first was:
T = Fc+ Fg
Fc=T-Fg
mv^2/r = 1500 -mg
V^2/4 =1500 - 10(cancelled out the masses)
v = 1500 -10(4) ~~~~(idk how to the square root in my calculator hopefully u get the idea)
v = 38.2 m/s
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The answer was wrong according to the textbook( 5.6m/s at the lowest point of the swing)
So I tried another way starting from the side
T = Fc
1500 = mv^2/r
1500 = 85v^2/4
1500(4)/85 (square root) = v
v= 1.823 m/s
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WHAT HAVE I DONE WRONG :c I used the equations I was taught but meeh please help

Last edited by a moderator: Nov 11, 2014
2. Nov 11, 2014

SteamKing

Staff Emeritus
How do you cancel out the masses and leave the 1500 unchanged? This is where your problems start.

It takes more than just memorizing some equations. You've got to get the math right as well.

Last edited by a moderator: Nov 11, 2014