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## Homework Statement

M1 and M2 are two masses connected as shown. The pulley is light (massless) and frictionless. Find the mass M1, given that M2 (3.5 kg) accelerates downwards at 3.35 m/s^2, θ is 35o, and μk is 0.25.

http://img525.imageshack.us/img525/7076/prob31fricpullplaneyi0.gif [Broken]

## Homework Equations

## The Attempt at a Solution

The total force (which is the total mass times the acceleration) is equal to the sum of the forces.

Forces:

Gravity = M1g

Normal = M1g(sinθ)

Applied = M1a

Kinetic Friction = μkM1a

g=9.81m/s^2

a(M1 + M2) = -M1g +M1g(sinθ) +M1a -μkM1a

M1a +M2a = M1g((sinθ)-1) +M1a -μkM1a

M2a = M1(g((sinθ)-1) -μka)

M1 = M2a/(g((sinθ)-1) -μka)

M1 = (3.5*3.35)/(9.81((sin35)-1) -0.25*3.35)

M1 = 11.725/(9.81(-.426)-0.8375)

M1 = -2.34 kg

A negative answer isn't even possible, but I tried putting in "2.34 kg" is an answer and that didn't work. I don't know what I'm doing wrong.

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