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Goofball Randy
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Homework Statement
Block A in the figure has a mass of 5.00kg , and block B has mass 12.0kg . The coefficient of kinetic friction between block B and the horizontal surface is 0.25.
What is the mass of block C if block B is moving to the right and speeding up with an acceleration 3.00m/s2 ?
Homework Equations
Friction = coefficient * normal force
F = ma
The Attempt at a Solution
I found the frictional force heading left (since block is going right). 0.25 * (12 * 9.81) = 29.43 N
The tension force on B is then just F = ma + friction force, so 12 * 3 + 29.43 = 65.43 N
And the acceleration of block C, which should also be 3 m/s2, gives the equation Ca = Cg - T, since the acceleration downwards is just gravitational force - tension force. So 3C = 9.81C - 65.43, C = 9.608kg
But this is wrong! And I don't know why :(
The textbook sucks too...pulleys aren't even so much as mentioned in the chapter we're in.
Edit: Tried accounting for A.
A is moving up at 3 m/s2.
So -3A = Ag - T
-3(5) = (9.81)(5) - T
T = 34.05 N
So then the total forces pulling left are 34.05 + 29.43 = 63.48N (A and friction). So the forces pulling right must equal that + 36 (F = (12)(3)) = 99.48N. So 3C = 9.81C - 99.48, C = 14.608kg
Still doesn't work :(
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