Tension of a string with a pulley

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To find the tension in a string connected to two masses over a frictionless pulley, the equations of motion for each mass must be established. The acceleration of the system was calculated to be 2.79 m/s². Using this acceleration, the forces acting on each mass were determined, leading to the correct expression for tension. The final calculation confirmed the tension value, resolving the initial confusion regarding the relationship between mass and weight. This approach effectively illustrates the dynamics of a pulley system with differing masses.
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Homework Statement


Two masses are connected by a string over a pulley as shown below. The incline is
frictionless and makes a 50 degree angle from the horizontal. If m1 = 3.00 kg and m2 = 8.00 kg, find the tension in the string.

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Homework Equations


F = ma

The Attempt at a Solution


I thought the tension in the string would be the same as the weight of m1, which is 29.4N, but that is not the correct answer. I am not sure what to try from here.
 
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m1 accelerates, so you need to take that into consideration.
First write up the equations of motion of the two blocks.
i.e. m1*a=...
and m2*a=...
 
I got that that a equals 2.79m/s², so:

m1*a = 3 * 2.79 = 8.37N
m2*a = 8 * 2.79 = 22.32N

Is that what you mean? Is that right?
 
Yes, and now you can express the tension of the string. m1*a=m1*g-T
 
That got me the correct answer! Thanks so much for your help!
 
Last edited:
The book claims the answer is that all the magnitudes are the same because "the gravitational force on the penguin is the same". I'm having trouble understanding this. I thought the buoyant force was equal to the weight of the fluid displaced. Weight depends on mass which depends on density. Therefore, due to the differing densities the buoyant force will be different in each case? Is this incorrect?

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