How Long Can the Climber Hang Before the Rock Falls?

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SUMMARY

The discussion centers on a physics problem involving a 65 kg climber and a 940 kg rock on an ice cliff, focusing on the climber's acceleration and the time before the rock falls. The climber's acceleration was incorrectly calculated as 0.127904 m/s² due to a sign error in the force equation. The correct approach involves recognizing that the climber's downward movement requires a negative acceleration in the equation FT - massclimber * g = -massclimber * a. The frictional force is determined using the formula Ff = Mu(k) * N, where Mu(k) is the coefficient of kinetic friction.

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Homework Statement



A 65 kg climber finds himself dangling over the edge of an ice cliff, as shown in the figure below. Fortunately, he's roped to a 940 kg rock located 51 m from the edge of the cliff. Assume that the coefficient of kinetic friction between rock and ice is 5.7×10−2. What is his acceleration, and how much time does he have before the rock goes over the edge? Neglect the rope's mass.

Homework Equations



Rock
FT - Ff = massrock * a
N = massrock * g

Climber
FT - massclimber * g = massclimber * a

The Attempt at a Solution



I solved for FT for the climber and then stuck this equation into FT in the rock equation. Then solved for a.

a = (g(massclimber - Mu(k) * massrock)) / (massrock - massclimber)

Plugging the numbers in the equation, i get a = 0.127904 m/s2 My homework tells me this is wrong and I can't figure out why. any help is appreciated!
 
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What's the force of friction?

What is the books answer btw?
 
Ff = Mu(k) * N or Mu(k) * massrock * g

it's actually homework on the computer and doesn't give me the answer. Just tells me mine is wrong and to try again!
 
figured it out

FT - massclimber * g = massclimber * a
should be
FT - massclimber * g = -massclimber * a
since the climber is moving downward
 

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