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Edexcel M5 12th June 2015 [Official Thread]

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Reply 60

Trinh Hong Khanh

Original post by Gome44

Yes

what if it does not start from rest?

Reply 61

Gome44

Original post by Trinh Hong Khanh

what if it does not start from rest?

No (I think) :smile:

Reply 62

jjpneed1

Quick query if anyone is awake

When working out the forces acting on the axis of rotation (X - mgcos. .., Y - mgsin... etc) what's a clear way to know which way the signs are? I know X acts towards O and Y is tangent to motion, but if I had a uniform rod rotating about an axis then aren't the weight and X both acting towards O? But this doesnt seem to be true, markscheme says mgcos - X = ..

June 2014 Q5 for reference

Reply 63

cogito.

Just leave your answers for both side. So the examiner will mark the correct one.

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Reply 64

Rainybird

Pretty easy paper compared to the normal. What did you guys think?

Reply 65

HashiramaSenju

Yup whats your answer ?

Reply 66

Rainybird

Struggling to remember answer.
1) a=3
2) F3 = (2, -1, -1), r =(1,0,1) + λ(2, -1,-1)
3) r = -(1/4)sect(cos2t+1)i
4) 2Mo
5) (2a/5g)?, 1/10 mg?
6) can't remember
7)2/5 ma^2, 2/5 Ma^2

Reply 67

HashiramaSenju

Got all the same except for 7a where i got 1/5

Reply 68

Rainybird

Original post by HashiramaSenju

Got all the same except for 7a where i got 1/5

They were the same because the density was half

what do you mean

Original post by HashiramaSenju

what do you mean

The mass of the hemisphere is M/2 so when you add the two MOI together you get the same as for the hemisphere.

Reply 71

Human156

I think I got the same answers! For q3 I simplified it to -(1/2)cost i, then for q6 I think I got something like a period of 2pi x sqrt (12a/7g) and J was m x sqrt(21ga), although I could be remembering wrong

Reply 72

Rainybird

Original post by Human156

Ahh I remember now, got them too :smile:

(edited 8 years ago)

Reply 73

HashiramaSenju

Original post by Rainybird

The mass of the hemisphere is M/2 so when you add the two MOI together you get the same as for the hemisphere.

i first got 2/5 then got confused and wrote it as 1/5 by calculating the desity incorrectly. Oh no ! how much do you think i will lose ?

Reply 74

Rainybird

1) a=3
2)a) F3 = (2, -1, -1)
b)r =(1,0,1) + λ(2, -1,-1)
3) r = -(1/4)sect(cos2t+1)i
4)2Mo
5)a)(2a/5g)
b)1/10 mg
6)a)2π sqrt(12a/7g)
b)m sqrt(21ag)
7)a) 2/5 ma^2
b)2/5 Ma^2

(edited 8 years ago)

Reply 75

Rainybird