AQA M2- June 2011

Yeah, length, radius, whatever, it's always metres.

Thanks.



June 10, can anyone help me with 8b. I don't understand why the markscheme says T=mgcos (15). And not T cos (15) =mg. How can the weight of the object be acting horizontally?

http://store.aqa.org.uk/qual/gce/pdf/AQA-MM2B-W-QP-JUN10.PDF

I can see it. Try not to think of ' cos ' as meaning horizontally all the time. It does in some cases but here it would'nt end up that way.

If you remember your trig you know Cos(x) = a/h
Now in this example the mg is acting downward and in order to form an equation with T you need mg acting in the same direction as T.
Can you see that T acts along the hypotenuse of part of the triangle ?
And can you also see that mg acts in the same direction as the adjacent ( directly down).

If it helps you then have a diagram where T is along the hypotenuse and mg is along the adjacent ( which you can do because they are both directly down)
Then its easy to see that to get mg acting in the same direction as T you must have

Cos (x) = a/h
Cos (x) = mg/T
mg cos (x) = T
and yeh x = 15.

Hope that helps.

.... not that I'm doing this Q but I was following your logic until you did the equations. You couldn't get mg cos (x) = T from cos (x) = mg/T

Hmm I think I've got it after looking at a moments question. If you think of MG acting in two directions you can get the bit of mg that is acting parallel to T. They must equal each other so mg cos 15 = t, and then solve for m.

Surely at Q it has energy 1/2*4*m + 3gm
And at P it has energy 1/2*m*v + gm(3-3cos theta)

But in the mark scheme it just has three energy terms, how come there is no GPE at the top ?

Has anyone got the specimen?

Not really can you just think of it as losing 3mg(1-cos theta ) of energy?

the specimen paper will be worse then tomorrow garanteed! try a different exam board for more questions!

Yeah but if I can do the specimen I'm sorted (ish... xD)

Just about to try it

Someone kindly posted it on this thread : http://www.thestudentroom.co.uk/showthread.php?t=1682725

If anyone wants it

Yeah but if I can do the specimen I'm sorted (ish... xD)

Just about to try it

Someone kindly posted it on this thread : http://www.thestudentroom.co.uk/showthread.php?t=1682725

If anyone wants it

Did you try it??

The question at the end is baffling me where its asks for h do you only consider energy between the top of the hill and the bottom just before the loop, does it have nothing to with loop?