Tension Force (should be easy)

[Angry Citizen]

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?

 

[PhanthomJay]

You ll have to attach the pic or better describe the setup. 3 pulleys? What side is rod connected? How many ropes?

 

[Angry Citizen]

Here you go.

 

[PhanthomJay]

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.

 

[asteriatic]

As a scientist, it is important to approach problems with a clear and logical mindset. It seems like you have already attempted to solve the problem using free body diagrams and the equation F=ma. However, it is important to double check your calculations and make sure you are using the correct units. In this case, the weights of the blocks are given in pounds, but the equation F=ma requires the use of mass in kilograms. Make sure to convert the weights to mass before solving for acceleration. Additionally, it may be helpful to draw a more detailed free body diagram, including all the forces acting on each block, to ensure that you are considering all the forces in your calculations. Remember to also consider the direction of the acceleration and the signs of the forces. I would recommend going through your calculations step by step and checking for any errors or missing factors. With a careful and systematic approach, I am confident that you will be able to solve this problem and arrive at the correct answer.