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## Homework Statement

A prism has the mass m with the angle x = 45°(look at the picture) placed on the ground without friction. The other prism, which has the same mass m, is placed above the first prism(the first prism is bigger). A horizontal force F is given to the second prism so the displacement with respect to the first prism is zero( or not moving). What is the friction between the two prism ( in F, m, and g). g = earth gravitational acceleration

The picture -> http://i28.tinypic.com/nycih4.jpg

## Homework Equations

[tex]F = m.a[/tex]

## The Attempt at a Solution

[tex]F.cosx - f - m.g.sinx = m.a[/tex]

Since the prism is not moving, so a = 0

[tex]F.cosx - \mu.m.g.cosx - m.g.sinx = 0[/tex]

[tex]F.cosx = \mu.m.g.cosx - m.g.sinx[/tex]

[tex]\mu = \fric{F}{m.g} + tanx[/tex]

Then i have no idea what to do next. I haven't even used the mass of the first prism. I also don't quite understand how the forces work so can somebody help me please?

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