RLangdon569
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I do not know how to do part a of this question, any guidance would be greatly appreciated. Thanks.
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RLangdon569
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ghostwalker
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(Original post by RLangdon569)
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Since you're dealing with a reaction on the wire and circular motion, that would suggest using formula for force to move in a circle.

You're going to need the velocity, when at an angle theta, so conservation of energy to get it in terms of the initial velocity.

And you're told that the initial veloicty is just sufficient to carry it to the top of the wire, so you can form an equation for the initial velocity.

Put it all together; lots of cancellation and you have theta. (Does work!)
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RLangdon569
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(Original post by ghostwalker)
Since you're dealing with a reaction on the wire and circular motion, that would suggest using formula for force to move in a circle.

You're going to need the velocity, when at an angle theta, so conservation of energy to get it in terms of the initial velocity.

And you're told that the initial veloicty is just sufficient to carry it to the top of the wire, so you can form an equation for the initial velocity.

Put it all together; lots of cancellation and you have theta. (Does work!)
Hi, thank you for the outline. Sorry if I am being obtuse but I calculated that initial velocity is sqrt(4ag). The equation for force would be T-mgcosTheta= maw^2 . Using conservation of energy, v = sqrt ( 2ag(2-costheta)). Not quite sure how to put this together. thanks
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ghostwalker
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(Original post by RLangdon569)
Hi, thank you for the outline. Sorry if I am being obtuse but I calculated that initial velocity is sqrt(4ag). The equation for force would be T-mgcosTheta= maw^2 . Using conservation of energy, v = sqrt ( 2ag(2-costheta)). Not quite sure how to put this together. thanks
In order:

I'd leave the initial velocity, u, as u^2 since you're using it in the KE of the conservation of energy equation.

You're told what T is in the question.

For force to move in a circle, I'd use mv^2/r rather than mr\omega^2 since we're getting velocity from the conservation of energy.


Again I'd leave v as v^2, for the same reason as for u, though your equation for v doesn't look correct - check the derivation.
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RLangdon569
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(Original post by ghostwalker)
In order:

I'd leave the initial velocity, u, as u^2 since you're using it in the KE of the conservation of energy equation.

You're told what T is in the question.

For force to move in a circle, I'd use mv^2/r rather than mr\omega^2 since we're getting velocity from the conservation of energy.


Again I'd leave v as v^2, for the same reason as for u, though your equation for v doesn't look correct - check the derivation.
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ghostwalker
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(Original post by RLangdon569)
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4 lines from the bottom is correct.

@ 3 lines from the bottom you've gone wrong.
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RLangdon569
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(Original post by ghostwalker)
4 lines from the bottom is correct.

@ 3 lines from the bottom you've gone wrong.
I see it now, silly mistake. 3costheta = 3/2, theta = Pi/3
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ghostwalker
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(Original post by RLangdon569)
I see it now, silly mistake. 3costheta = 3/2, theta = Pi/3
Agreed.
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RLangdon569
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(Original post by ghostwalker)
Agreed.
sorry to be a pain, but I assumed for part ii that I would be using the relationship v=rw , however that doesn't seem to work out.
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RLangdon569
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(Original post by ghostwalker)
Agreed.
Appreciate the guidance and help you give sincerely.
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(Original post by RLangdon569)
sorry to be a pain, but I assumed for part ii that I would be using the relationship v=rw , however that doesn't seem to work out.
Seems fine to me. Post working/thoughts.
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RLangdon569
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(Original post by ghostwalker)
Seems fine to me. Post working/thoughts.
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ghostwalker
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(Original post by RLangdon569)
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Yes.
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RLangdon569
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(Original post by ghostwalker)
Yes.
Is part iii a case of v^2 =u^2 + 2as ?
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RLangdon569
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(Original post by ghostwalker)
Yes.
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(Original post by RLangdon569)
Is part iii a case of v^2 =u^2 + 2as ?
Is acceleration constant in this scenario?
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RLangdon569
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(Original post by ghostwalker)
Is acceleration constant in this scenario?
No
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RLangdon569
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(Original post by ghostwalker)
Is acceleration constant in this scenario?
Would you please offer your guidance how to go about part iii ? Thanks a lot
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(Original post by RLangdon569)
No
So, suvat doesn't apply. How else might you get the angular acceleration?
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