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Pulley problem with frictionless ropes

  • Thread starter Taz.
  • Start date
  • #1
20
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Homework Statement


In the diagram, the pulley is frictionless and the ropes are massless. You are given that m1 = 10.0 kg and m2 = 29.5 kg.

Calculate the acceleration of m2 downwards.

What is the magnitude of the tension in the string?


Homework Equations



sum of F= M*A



The Attempt at a Solution



I tried doing a free body diagram and solving for A but I still can't find the tension...
 

Answers and Replies

  • #2
1,198
5
You should post a picture of the pulley layout to make the problem clear.
 
  • #3
20
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QLacL.png
 
  • #4
1,198
5
OK, you have written Newton's Law. Draw a free body diagram of each weight calling the tension in the rope T. You should have two equations. Let's see them.
 
  • #5
20
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m2:

force of tension going up
force of gravity going down

t1-w=ma

m1: same thing ...
t1-w=ma
 
  • #6
1,198
5
Let's use some subscripts because the masses/weights are different:

T - w1 = m1 * a

T - w2 = m2 * a

Looking at what you've written, you'll need to define what w1 and w2 are. Also, you have a single variable for acceleration. But the accelerations are in opposite directions so what must be done?
 
  • #7
20
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So I have w1 and w2 and I have m1 and m2. Whats missing is T and A. Can I just solve for A or T ?
 
  • #8
1,198
5
So I have w1 and w2 and I have m1 and m2. Whats missing is T and A. Can I just solve for A or T ?
Yes you can but if you do you'll get an incorrect result. You have an error in one of your equations. Acceleration, like 'g', has a direction associated with it.
 
  • #9
1,198
5
Signing off for today.
 

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