Angle for Impending Motion on Inclined Plane with Attached Blocks

[physicsss]

The 8 kg block A is attached to link AC and rests on the 12-kg block B. Knowing that the coefficient of static friction is 0.20 between all surfaces of contact and neglecting the mass of the link, determine the angle for which motion of block B is impending.

Can someone check my equations and see if they are OK? There's something screwy with the numbers I'm pluggin in so if you can tell me what you should get, I will be grateful. Thanks.

Link to my work: http://img507.imageshack.us/img507/9884/img0801copy2bm.jpg

 

[lightgrav]

For impending motion, block B has
Sum of F parallel = - T + 2.5 W_A sin(theta) - mu N - F_1 cos(theta) = 0 .

Somehow you forgot to sum the Forces in that direction?

 

[physicsss]

The equation or the pluggin in of the numbers?

 

[lightgrav]

I didn't see any Sum of Forces equation for block B
in the parallel-to-the-ramp direction (perp to N).

 

[physicsss]

Why do I need it?

 

[lightgrav]

WHAT? That's the direction that the acceleration is to occur in!

The perp-to-ramp component Force Sum is just to get the Friction -
if the ramp was frictionless you wouldn't have needed it at all!

 

[physicsss]

That's the last equation labeled translational force...

 

[physicsss]

anyone? :-/