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# M4 help!!! Report awarded

1. Self teaching m4 so any help would be greatly appreciated.I feel like the form the question requires is incorrect and the cos (theta/2) should instead be sin (theta/2) but I'm not sure.

A uniform rod AB of mass m and length 2a is free to rotate in a vertical plane about the end A. A light elastic string of modulus kmg and natural length a has one ebd attached to B and the other end fixed to a point O which is vertically above A such that OA=2a. Show that when AB makes an angle theta with the dowand vertical and the string us streched the potential energy of the system is given by

V=mga[(4k-1)costheta-4kcos (theta/2)]+constant

Also please include diagram if possible
2. (Original post by Sapereaude45)
Self teaching m4 so any help would be greatly appreciated.I feel like the form the question requires is incorrect and the cos (theta/2) should instead be sin (theta/2) but I'm not sure.

A uniform rod AB of mass m and length 2a is free to rotate in a vertical plane about the end A. A light elastic string of modulus kmg and natural length a has one ebd attached to B and the other end fixed to a point O which is vertically above A such that OA=2a. Show that when AB makes an angle theta with the dowand vertical and the string us streched the potential energy of the system is given by

V=mga[(4k-1)costheta-4kcos (theta/2)]+constant

Also please include diagram if possible

Post some working if you'd like someone to check.

I got the extension as

And here's a diagram, though you should have that correctly yourself:

3. I did exactly that.However Ihad my angle t in the wrong place-this was an issue I had in m2 aswell. Where should I put the angle if it says with the donward vertical? Sorry for what should seem obvious but I have no teachers helping me with this module
4. (Original post by ghostwalker)

Post some working if you'd like someone to check.

I got the extension as

And here's a diagram, though you should have that correctly yourself:

Sorry reply above phone's playing up.
5. (Original post by Sapereaude45)
I did exactly that.However Ihad my angle t in the wrong place-this was an issue I had in m2 aswell. Where should I put the angle if it says with the donward vertical? Sorry for what should seem obvious but I have no teachers helping me with this module
The downward vertical through a point, is the vertical line starting at that point and going downwards, This forms one of two lines that define the angle.

In this case we have the angle at A, defined by the line from A to B, and the line from A going vertically downwards. Hence....

Does that cover it?

Edit: Signing off for the night.
6. (Original post by ghostwalker)
The downward vertical through a point, is the vertical line starting at that point and going downwards, This forms one of two lines that define the angle.

In this case we have the angle at A, defined by the line from A to B, and the line from A going vertically downwards. Hence....

Does that cover it?

Edit: Signing off for the night.
Yep all covered! Managed to get the correct form the question required too.

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