# Tension on the String

• minimario

F=ma

## The Attempt at a Solution

A FBD on the bottom block gives tension in C is equal to Mg. Then, a FBD on the middle block should give T_b-T_c=0, so tension on B should also be equal to Mg. Finally, a FBD on the top block gives the tension on A is equal to Mg.

But this is not correct, what did I do wrong?

... so tension on B should also be equal to Mg.
Really? You might want to rethink that.

What are the forces acting on the middle block? Are they not only tension in B and tension in C?

Draw a free body diagram of the middle block. Show the forces acting on that block. What are they?

Chet

For your 2nd FBD, on the middle block, you forgot to include the Weight of that block. Same for the FBD on the top block.

What are the forces acting on the middle block? Are they not only tension in B and tension in C?
Yes, but how does that relate to the answer to the you are looking for. Are you looking for the forces on a single block or the tension on the various strings? Suppose B was a rigid rod instead of a string. What would that do to your perception of the tension in string A ?

Ok, thanks. I got it now. The FBD on B should be T_b=T_c+Mg

Chestermiller