# Newton’s law question (pulley)

**1. The problem statement, all variables and given/known data**

Block A has a weight of 400N and block B has a weight of 100N. The coefficient of friction between all surfaces of contact are μ

_{s}= 0.7 and μ

_{k}= 0.2.

Knowing that θ = 60°, determine the acceleration of block A and the tension in the cord. Assume block A is moving downwards.

I know I should be solving for the acceleration but I figured if I get the tension I could use ∑F = ma on block B to get the acceleration there and that would be the same acceleration on block A.

**2. Relevant equations**

∑F = ma

**3. The attempt at a solution**

(BLOCK A)

took the inclined plane and it’s normal as the axis and used Newton’s equation on the perpindicular axis to get the normal (N – Wcosθ = 0) and got N = 200N. Then used the plane’s axis at the moment the tension force equals the static friction (Wsinθ – 2T – μ_{s}N = 0) but I got 103.7N as the answer when it should be 127N and I don’t know what my mistake is.

http://ift.tt/1iKugWI

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