Dependent motion with ropes question

[JustinLiang]

Homework Statement

I attached the problem with my attempt. I think the geometry I used is correct but I am getting the wrong answer. When I take the flip Va/V (as shown in my attempt) I get the right answer. I am not even sure if I can relate velocity with a triangle.

The method I used is based on the fact that Sa + Sb = L1 so when you take the time derivative you get Va = -Vb.

 

[ehild]

X=S_A cos(theta). As X increases in the rate of 1.5 m/s, both S_A and theta change. It is not true that V=V_A.

Write out Y_B in terms of X, and find the derivative with respect the time. ehild