Finding Acceleration of Two blocks connected by a string.

[shinify]

1. Two blocks made of different materials connected together by a thin cord, slide down a plane ramp inclined at an angle θ to the horizontal. The masses of the blocks are m_A and m_B and the coefficients of friction are μ_A and μ_B.

PART A
If μ_A < μ_B, determine a formula for the acceleration of block A in terms of m_A, m_B, and θ.
PART B
If μ_A > μ_B, determine a formula for the acceleration of block A in terms of m_A, m_B, and θ.


3. I got Part A right, of which a_{A, 1}= (m_Agsinθ+m_Bgsinθ-_Am_Agcosθ-μ_Bgcosθ)/(m_A+m_B)

For Part B, I attempted it to solve it, and got the same answer as I did in Part A, yet MasteringPhysics says this is incorrect. Am I doing anything wrong? "The correct answer does not depend on the variables: m_A, m_B, or μ_B. "

Thanks for the help in advance.

 

[Doc Al]

Hint: Do the blocks have the same acceleration?

 

[shinify]

Oh, got it. I simply assumed that if μ_A<μ_B, then the blocks would end up touching each other and have the same acceleration;

I see now that's not the case. I got a_{A, 2}= g(sinθ- μ_Acosθ). Thanks for your quick response and help, Doc Al!