Newtonian Mechanics: simultaneous equations

AI Thread Summary
The discussion focuses on solving a physics problem involving two blocks connected by a cord over a frictionless pulley. The user seeks assistance with deriving the acceleration equations for both blocks and the tension in the cord. They successfully manipulate the equations, ultimately arriving at the correct formula for acceleration, a = mg/(M + m). The conversation emphasizes the importance of correctly identifying and substituting variables in simultaneous equations. The user expresses satisfaction with their final solution and acknowledges the learning process involved.
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Homework Statement


Figure 5-12 shows a block S (the sliding block) with mass
M 3.3 kg. The block is free to move along a horizontal
frictionless surface and connected, by a cord that wraps over
a frictionless pulley, to a second block H (the hanging
block), with mass m 2.1 kg. The cord and pulley have neg-
ligible masses compared to the blocks (they are “massless”).
The hanging block H falls as the sliding block S accelerates
to the right. Find (a) the acceleration of block S, (b) the ac-
celeration of block H, and (c) the tension in the cord.

Homework Equations


Block S:
Tx=ma (on the X axis)

Block H:

T-mg=-ma (y axis)

The Attempt at a Solution


I understand the theory and question, my problem lies with my math skills. Because of the two unknown variables you can solve them simultaneously, however the sample problem assumes I remember how to do it!

I want to understand how you can mathematically go from the two equations on top to a=(m/M+m)g on the y axis.
Thank you for the help!
 
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To avoid confusion you need to use M and m in your relevant equations.
Also note that what you've called Tx is equal to what you've called T (and of course a is the same also) so you can plug one equation into the other and solve for a.
 
After playing around with the equations I got it. Thanks for the help! I should pay more attention to the variables. :D

I ended up going like:
T-mg=-ma -----> T=-ma+mg
T=Ma -----> (plug in eqquation number 1) -ma+mg=Ma ----->Ma+ma=mg------->a(M+m)=mg----->a=mg/M+m

Would this set up be okay?
 
That looks right. Good work.
 
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