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C2 Trig questions

Please can some one help me with the trig questions.
Please help me with Q11
thank you in advanceIMG.jpg
Original post by bigmansouf
Please can some one help me with the trig questions.
Please help me with Q11
thank you in advanceIMG.jpg


Just try it and see. (Through how many will it have turned when it's halfway round? How about a quarter of the way round, if that's hard to visualise?)
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Avatar for Kate2996
Kate2996
Original post by bigmansouf
Please can some one help me with the trig questions.
Please help me with Q11
thank you in advanceIMG.jpg


If it has rolled its whole perimeter then it must have rolled 360° so what is that in radians?

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Reply 3
Avatar for bigmansouf
bigmansouf
OP
20
I have tried it 360 degrees in radians is 2pi but the book says 4pi which confuses me.
A quarter is 1/2(pi) which is 90 degrees.
but I dont understand how it ended up with 4pi as the answer

thanks for the help
Original post by bigmansouf
I have tried it 360 degrees in radians is 2pi but the book says 4pi which confuses me.
A quarter is 1/2(pi) which is 90 degrees.
but I dont understand how it ended up with 4pi as the answer

thanks for the help


OK, this got me - 4pi is right. Let's imagine you had two mugs (so you've got a handle on one of them, to mark its direction) instead of two coins. Pretend the handle can move through matter, just so it does't collide with the mug.

Start out with the handle of the moving mug pointing directly outwards. Now, when the mug has got halfway round, the rim must have travelled through pi radians, so by halfway round, then handle must be pointing directly into the stationary mug. That is, a complete turn has happened on the way round. Try it with two actual mugs to see: it's really counterintuitive.
Original post by bigmansouf
I have tried it 360 degrees in radians is 2pi but the book says 4pi which confuses me.
A quarter is 1/2(pi) which is 90 degrees.
but I dont understand how it ended up with 4pi as the answer

thanks for the help


A better way someone's just shown me: consider the system fixed not about one coin, but around the contact point between the coins. As one coin makes a full rotation, the other must also rotate the same amount relative to the contact point; hence the total that either coin rotates relative to the other is 2 rotations, or 4pi.
(edited 8 years ago)
Reply 6
Avatar for bigmansouf
bigmansouf
OP
20
thank you very much it has helped me to understand it fully.

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