AQA A2 MM2B Mechanics 2 – 27th June 2016 [Exam Discussion Thread]

Scroll to see replies

NEED HELP WITh QUESTION 4 JAN 11 M2 PART C AND D

With part c just set up a diagram using the centre of mass you have worked out and then use trig. Part d is just a moments question where you have to take moments about P in order to work out the mass.

Reply 41

misslili118

Original post by JC25

I used a diagram but i keep getting arc tan 19.4/21.1 , i guess i have the wrong diagram?

Reply 42

JC25

Original post by misslili118

I used a diagram but i keep getting arc tan 19.4/21.1 , i guess i have the wrong diagram?

Maybe try the diagram again?

Reply 43

misslili118

Original post by JC25

Maybe try the diagram again?

Thank you so much!

Reply 44

username1824647

Original post by misslili118

Thank you so much!

i am stuck at this question too, markscheme says 24.6 for the angle i keep getting 8.45 because i used tan theta = 19.4/8.45
d
did u manage it?

Reply 45

misslili118

Original post by Husssein

i am stuck at this question too, markscheme says 24.6 for the angle i keep getting 8.45 because i used tan theta = 19.4/8.45
d
did u manage it?

its arctan 8.8/19.4 , youve got your sides the other way round

Reply 46

username1824647

Original post by misslili118

its arctan 8.8/19.4 , youve got your sides the other way round

OMD!, it was a school boy error silly mistake, my method was tan theta = 19.4/8.8 and take that theta away from 90 which gives correct answer but i mustve put it wrong in calc or summink thanks anyways

Reply 47

misslili118

Original post by Husssein

no problem , i still cant get d around my head

Reply 48

misslili118

HELPPPPPPPPP : jun 11 Q8 b .. why is it 0.5mu^2= 0.5mv^2 + mga(1+sintheta) and not just 0.5mv^2 + mgasintheta?? why is there an extra mga on the markscheme??

Reply 49

RockyG

Because the height of b is a+asintheta hence a(1+sintheta)

Reply 50

TheKian

June 13 question 9)a)i) I used T=lambda*x/original length where x is 0.5, but apparently it's 2.5 and I can't understand why

Reply 51

mamounaltayeb

ImageUploadedByStudent Room1466948657.032008.jpg

Can someone please explain how to do 8b , I've had a nightmare with it

Posted from TSR Mobile

Reply 52

mamounaltayeb

Original post by RockyG

Because the height of b is a+asintheta hence a(1+sintheta)

Why is it not asintheta since the radius is A

Posted from TSR Mobile

Reply 53

EB88

Original post by TheKian

June 13 question 9)a)i) I used T=lambda*x/original length where x is 0.5, but apparently it's 2.5 and I can't understand why

The new length of the string is 5.5 m because from A to O it's 3.5 m and from O to B its 2 m, so the extension is 5.5 - 3 = 2.5

Reply 54

RockyG

Original post by mamounaltayeb

Why is it not asintheta since the radius is A

Posted from TSR Mobile

Because the distance from b to the bottom of the circle is more than a , asintheta more so its total distance from the bottom is a + a sintheta :smile:

Reply 55

TheLifelessRobot

For part b in this question in the mark scheme when resolving radially it uses R + mgcos60 = mv^2/r which means that the reaction force acts towards the centre of the circle. My reason of thinking was that the reaction force would act in the opposite direction so that it would act outwards (mgcos60 - R = mv^2/r), directly away from the centre of the circle. Can someone explain why R acts towards the centre of the circle?

m2.jpg60.8KB

Reply 56

snimkar

Original post by TheLifelessRobot

Centripetal force causes the reaction to act inwards.

Reply 57

rainbowtwist

Original post by Mm68

Can someone confident with moments tell me their technique, my teacher has taught me a variety of methods and I'm getting them confused, mainly for your generic ladder question. I mainly don't understand which way to resolve the forces, been taught in the direction of the line, perpendicular to line, vertical, horizontal, and now I'm getting muddled.

I always resolve vertically, then horizontally and then take moments about a point

Reply 58

bartbarrow

Original post by mamounaltayeb

Can someone please explain how to do 8b , I've had a nightmare with it

Posted from TSR Mobile

For the next part you just set the answer to 0 to get sin(theta) = 5/6

EDIT: Ignore the one that is under 'attached thumbnail', the one above is the correct one