# Physics Help!

• Feb 22nd 2010, 02:23 PM
elexis10
Physics Help!
I need help with the current problem

Because the block is not moving, the sum of the y components of the forces acting on the block must be zero. Find an expression for the sum of the y components of the forces acting on the block, using coordinate system b.

Express your answer in terms of some or all of the variables http://session.masteringphysics.com/render?var=F_n, http://session.masteringphysics.com/render?var=F_f, http://session.masteringphysics.com/render?var=F_w, and http://session.masteringphysics.com/render?var=theta.

http://i86.photobucket.com/albums/k1...s/MFS_1l_1.jpg

Thanks!
• Feb 22nd 2010, 02:37 PM
icemanfan
Because the sum of the forces on the block is zero, you must have $F_n + F_f + F_w = 0$.

Thus, $F_n + F_f = -F_w$.

Now, using coordinate system b, $F_w = <0, -mg>$, where m is the mass of the block and g is the acceleration due to gravity. Also, you know that $F_n = <-\lambda \sin \theta, \lambda \cos \theta>$, $F_f = <\omega \cos \theta, \omega \sin \theta>$, and $\lambda^2 + \omega^2 = (mg)^2$. Can you figure out how to solve for $\lambda$ and $\omega$?