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uph0
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Homework Statement
A block of mass 20 kg is pushed against a vertical surface (see picture). The coefficient of friction, μ, between the surface and the block is 0.2. If θ = 30°, what is the minimum magnitude of P to hold the block still?
Homework Equations
f = force of friction = μN
The Attempt at a Solution
I drew a force body diagram and got equations for x and y.
x: N - Psinθ = 0
Y: -pcosθ + mg + f = may
N = psinθ
so f = μ psinθ
I put f = μ psinθ into the y equation
so i get
-pcosθ + mg + μpsinθ = may
I'm stuck here. I want to find P but I don't know the acceleration.