A level physics - conical pendulum

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rick780567
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doing this isaac physics question on circular motion, can anyone help

The bob of a conical pendulum is attached to a fixed point A,A by a string of length 50, c, m,50cm and is moving in a circular path, as shown in the diagram. A smooth horizontal table is placed below A,A so that the bob of the pendulum can describe a circular path of radius 30, c, m,30cm on the table.

A conical pendulum.
Figure 1: A conical pendulum supported by a table

Find the angular speed of the bob when the normal reaction force, R, from the table goes to 0, N

i couldnt copy the image but all the information is given in the question
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Pangol
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(Original post by rick780567)
doing this isaac physics question on circular motion, can anyone help

The bob of a conical pendulum is attached to a fixed point A,A by a string of length 50, c, m,50cm and is moving in a circular path, as shown in the diagram. A smooth horizontal table is placed below A,A so that the bob of the pendulum can describe a circular path of radius 30, c, m,30cm on the table.

A conical pendulum.
Figure 1: A conical pendulum supported by a table

Find the angular speed of the bob when the normal reaction force, R, from the table goes to 0, N

i couldnt copy the image but all the information is given in the question
If the reaction force is zero, then the bob doesn't count as being in contact with the table at all. This makes it a conventional conical pendulum question, where you can just think about it as moving as if the table wasn't there. Do you know how to do standard conical pendulum questions?
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rick780567
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(Original post by Pangol)
If the reaction force is zero, then the bob doesn't count as being in contact with the table at all. This makes it a conventional conical pendulum question, where you can just think about it as moving as if the table wasn't there. Do you know how to do standard conical pendulum questions?
i dont have any clue of how to answer this question
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Pangol
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(Original post by rick780567)
i dont have any clue of how to answer this question
The only forces acting on the bob are its weight and the tension in the string. There might be a reaction force from the table, but you are told to consider the case when this is zero (I expect this won't be the case in the later parts of the question). You have to resolve vertically and horizontally. Bear in mind that there is no vertical acceleration (since the bob moves in a horizontal plane), but there is horizontal acceleration (since the bob is moving in a circle). Both of your resolving equations will include the tension, which you can then eliminate - the only remaining term should be one involving the angular speed (or possibly linear speed depending on how you do it, but you can find the angular speed from that).

If you have never seen a conical pendulum problem before, it's probably best to read through a worked example first.
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