Interacting forces/inclined plane problem

[fsm]

I am having a promlem figuring the acceleration:

Figure shows a block of mass m resting on a 20 degree slope. The block has coefficients of friction mu_s =0.80 and mu_k =0.50 with the surface. It is connected via a massless string over a massless, frictionless pulley to a hanging block of mass 2.0 kg.

If this minimum mass is nudged ever so slightly, it will start being pulled up the incline. What acceleration will it have?

My equation I have is:

T-f_k-(mg*sin(theta))=m*a

where f_k=u_k*(mg*cos(theta))

I keep getting the answer wrong. Is it my formula?

 

[PhanthomJay]

I am having a promlem figuring the acceleration:

Figure shows a block of mass m resting on a 20 degree slope. The block has coefficients of friction mu_s =0.80 and mu_k =0.50 with the surface. It is connected via a massless string over a massless, frictionless pulley to a hanging block of mass 2.0 kg.

If this minimum mass is nudged ever so slightly, it will start being pulled up the incline. What acceleration will it have?

My equation I have is:

T-f_k-(mg*sin(theta))=m*a

where f_k=u_k*(mg*cos(theta))

I keep getting the answer wrong. Is it my formula?

Formula is looking good, real good. However, it can't be solved alone, since there are 3 unknowns (T, m, and a). You need a couple of more equations. How about an FBD of the 2 Kg mass after the nudge?? And, what can you conclude from the condition of the system BEFORE it was nudged??

 

[fsm]

I know the tension and mass. I'm trying to figure out the acceleration. When I use the above formula I get a wrong answer.

 

[OlderDan]

I know the tension and mass. I'm trying to figure out the acceleration. When I use the above formula I get a wrong answer.

How do you know the tension and how do you know the mass? Neither of them is given in the problem. Perhaps it is what you think you know that is leading you in the wrong direction.