M1 OCR (Not MEI) Exam - 12/06/2014

Hey.. I've literally just explained that above. You can have a look!

This is what I did...



Posted from TSR Mobile

No it should be drawn from head to tail (not starting from the same point). You have calculated something else. This makes it clear

There ya go

Posted from TSR Mobile

You draw up a vector diagram like this one.

To find the angle you should use the sine rule. There are two unknown angles - give one in terms of the other and solve them

To find the magnitude of the resultant force simply use the cosine rule. It's simple if you know basic trigonometry

Alternatively you could resolve the forces into their perpendicular components and using Pythagoras find the magnitude of the resultant. Then using tan ratio the angle needed could be found

thanks, but in the solutions the answers are 0.49 and 0.849
and I cant seem to follow what you're doing

Ohh.. But how can it be x+y.. aren't those corresponding angles.. and be the same?

If you look at your diagram how do you know if it's going one way or the other? Like is the resultant acting from the head of the 7N force to the head of the 5N force or the other way?

Well when you're drawing a vector diagram for two forces it becomes a parallelogram. The rule is that the head of the first force should be the tail of the second force and carrying on. It's the vector addition law.

can anyone explain why on question 3 part iii they minus the 40 from 360 degrees to find the bearing.
Any tips for working out the bearing of the resultant??

oh sorry thought I sent the link , June 2010
how did they work out the bearing to be 320?

what is the difference between limiting equilibrium and limiting friction?

what is the difference between limiting equilibrium and limiting friction?

Limiting equilibrium.. is that the particle/object is JUST about to move

Limiting friction is the max possible value of friction on the object/particle..

If the friction is limiting, but the object is still stationary, the object will be in limiting equilibrium..

http://www.ocr.org.uk/Images/63190-question-paper-unit-4728-01-mechanics-1.pdf

question 2) i) about momentum i done
(0.4x3)+(-1.5x0.6) = (-0.1x0.4) + (-0.6v)
and i get 0.567 as v

However...in the markscheme it has 0.433 as v
http://www.ocr.org.uk/Images/61377-mark-scheme-unit-4728-mechanics-1-june.pdf

And ive figured out you get that if you make the RHS values both positive, but in the mark scheme all it said is that they should have the same sign!? How am I meant to know whether to make them negative or positive?

Did you consider the direction?