# I was set a question and need help

My math teacher set me a question on friction, knowing I was interested in physics. But he never gave me the solution, So i'm not sure if my working is correct. Any help is appreciated.

Question: A brick of mass 1.2 KG is sliding down a rough plane which is inclined at 25 degrees to the horizontal. Given that the acceleration is 0.3ms^-2, Find the coefficient of friction between the brock and the plane.

My answer: Using F = ma

R - 1.2g cos25 = 1.2 x 0
R = 1.2g cos 25
R = 10.66 N

1.2g sin25 - F = 1.2 x 0.3
F = 1.2g sin25 - 1.2 x 0.3
= 4.61 N

Therefore F = 'mu'R
4.61 = 'mu' x 10.66
4.61/10.66 = 'mu'
'mu' = 0.43

Many thanks, Alex

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