hb763
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Hi all,

Can anyone help me with this one?

A mass of 50 grams hangs in equilibrium on a string. The mass is pulled aside and upwards by a force of 0.3 N which makes an angle of 30° with the horizontal.
Find the angle that the string makes with the vertical and the tension in the string.

Why is the angle not 60? Surely 90-30 = 60? I have no problems with finding the tension of the string once I have the angle - just so confused on the angle of it! Just need someone to push me in the right direction here Thank you in advanceeeeee x
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Anonymouspsych
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(Original post by hb763)
Hi all,

Can anyone help me with this one?

A mass of 50 grams hangs in equilibrium on a string. The mass is pulled aside and upwards by a force of 0.3 N which makes an angle of 30° with the horizontal.
Find the angle that the string makes with the vertical and the tension in the string.

Why is the angle not 60? Surely 90-30 = 60? I have no problems with finding the tension of the string once I have the angle - just so confused on the angle of it! Just need someone to push me in the right direction here Thank you in advanceeeeee x
Draw a clear diagram and consider the equilibrium of forces via a force triangle.
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hb763
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Resolving:
R(horizontal): 0.3cos30
R(vertical): 0.3sin30 - 5g
Then tried drawing a triangle with this resultant force but unsure what to do with it?
Draw a clear diagram and consider the equilibrium of forces via a force triangle.
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Anonymouspsych
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(Original post by hb763)
Resolving:
R(horizontal): 0.3cos30
R(vertical): 0.3sin30 - 5g
Then tried drawing a triangle with this resultant force but unsure what to do with it?
No don't resolve, just draw a force triangle.

So draw a free body diagram of the 3 forces acting on the mass. And put these forces tip to toe forming a closed triangle.
Then you can find the angle and tension using trigonometry etc.

You can do it by resolving too but it's better to do it this way.
There is no resultant force acting on the mass, it's in equilibrium hence the closed force polygon.
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hb763
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I have never drawn a force triangle in my life to be honest, have always been taught to resolve in both directions.
(Original post by Anonymouspsych)
No don't resolve, just draw a force triangle.

So draw a free body diagram of the 3 forces acting on the mass. And put these forces tip to toe forming a closed triangle.
Then you can find the angle and tension using trigonometry etc.

You can do it by resolving too but it's better to do it this way.
There is no resultant force acting on the mass, it's in equilibrium hence the closed force polygon.
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Anonymouspsych
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(Original post by hb763)
I have never drawn a force triangle in my life to be honest, have always been taught to resolve in both directions.
Well in that case you're going to have to solve two simultaneous equations coming from horizontal and vertical equilibrium. You can't find the angle on its own and then find the tension which seems like what you're trying to do. Let θ = angle tension makes with vertical and T=tension in string:

Horizontally: 0.3cos(30) = T sinθ

Vertically: Tcosθ +0.3sin(30) = mg

You can solve the above equations simultaneously and find what θ and T are
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hb763
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Ahhhhhh ok I understand now thank you so much. So I'm solving the string as an unknown 3rd force?
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Anonymouspsych
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exactly
(Original post by hb763)
Ahhhhhh ok I understand now thank you so much. So I'm solving the string as an unknown 3rd force?
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ck4203
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What's the answers?
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(Original post by hb763)
Ahhhhhh ok I understand now thank you so much. So I'm solving the string as an unknown 3rd force?
Do you still have the answers to these?
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