Atwood at an incline accelerating down

[Enginearingmylimit]

Homework Statement

A system comprising blocks, a light frictionless pulley, a frictionless, incline, and connecting (“massless”) ropes is shown in the figure. The 9 kg block accelerates downward when the system is released from rest. What is the tension in the rope connecting the 6 kg and 4 kg block?

Relevant Equations

F = ma
Fgy = 9.8 × m

Both myself and my TA gave up, but we found acceleration of the system

9g - 4gsin(30) = 13a
a=5.27m/s^2

 

[kuruman]

Yes, you do need to find the common acceleration of the masses first but you have the wrong equation for that. The straightforward way to find the acceleration is to draw two separate free body diagrams (FBD) and get two separate equations, one for the two masses on the incline and one for the hanging mass. Once you have the common acceleration, you can find the tension between the masses by drawing a FBD for the 6.0-kg mass.

 

[haruspex]

Unfortunately the image of the question is cropped at the right side. As a result, the answer to the question as posted is "a rope".