How Do You Find the Acceleration of Block A Given These Weights?

AI Thread Summary
To find the acceleration of block A, given weights of W_A = 120 lb and W_B = 20 lb, the equations of motion are set up using F=ma. The user initially attempted to solve using free body diagrams but received an incorrect answer, expecting 4.02 ft/s^2. Feedback indicates that there may be errors in the signs used for the forces acting on block B and in the mass units, which should be in slugs. Clarification on the setup, including the number of pulleys and ropes, is necessary for accurate calculations. Correcting these issues should lead to the right acceleration value for block A.
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Homework Statement



The weights of the blocks are W_A = 120 lb and W_B = 20 lb, and the surfaces are smooth. Find the acceleration of block A.

[A picture is shown. Block A is connected via rod to a pulley, and Block B is hanging from the pulley via cord.]

Homework Equations



F=ma

The Attempt at a Solution



This is embarrassing. I feel like I'm having a brain fart. I did free body diagrams showing that T-W_B=(M_A)a, and that T=(M_B)a, and substituted them into equations, but the book says it's the wrong answer; I should be getting 4.02 ft/s^2, but I'm getting something different. Any help please?
 
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You ll have to attach the pic or better describe the setup. 3 pulleys? What side is rod connected? How many ropes?
 
Here you go.
 

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I don't know what answer you are getting, but your signage is wrong when looking at
Block B. also make sure your mass unit are in slugs.

Edit: you also used M_B in your second equation when you should have used M_A.
 
Last edited:

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