Deriving Coefficient of Static Friction for Inclined Textbook and Coin

[nerdonsite]

ok, our class got an assignment where we have to derive an equation for coefficient of static friction between our textbook (inclined at an angle theta) and a coin. The vale of the angle and the mass of the coin are not given. I have come up with the following equation and need to know if it is correct.

u = Ff(static)/Fnormal
*using components of the force of gravity, i determined Ff to be FgxSINxTheta and Fnormal to be FgxCOSxtheta
so,
u = FgxSINxTheta/FgxCOSxtheta

does this seem correct?

thanks for looking.

 

[tony873004]

mg sin\theta is the gravitational force down the ramp, so
-(mg) sin\theta is the force of static friction.

mg cos\theta is indeed the force normal

\mu=\frac{F_{friction}}{F_{normal}}

\mu must be positive, so
\mu=\mid \frac{-(mg) sin\theta}{(mg) cos\theta}\mid

Which looks exactly like what you got except you call it Fg and I called it mg

 

[nerdonsite]

thanks, i just asked a friend and he got the same thing, so this must me right