Mr M's OCR (not OCR MEI) Mechanics 1 Answers January 2013

1. 15 N and 036.9 degrees (5 marks)

2. (i) Show v = 0 (3 marks)

(ii) Show a = 9 (3 marks)

3. (i) T= 1.30 (3 marks)

(ii) R = 1.68 (3 marks)

(iii) u = 1.96 (4 marks)

4. (i) t = 3 and t = 6 (2 marks)

(ii) -13.5 m/s (4 marks)

(iii) Show change in direction of motion (2 marks)

5. (i) a = 4.9 and T = 1.47 (4 marks)

(ii) m = 0.1 (3 marks)

(iii) 0.5 m (4 marks)

(iv) (a) T = 7.84 N (2 marks)

(b) T = 4.9 N (1 mark)

6. (i) v = 0.4 m/s (3 marks)

(ii) (a) Q is in motion with a velocity of 1 m/s (4 marks)

(b) 2 seconds (4 marks)

(c) Sketch correct graphs (4 marks)

7. (i) v = 6.87 m/s and t = 0.337 s (7 marks)

(ii) (a) Show P does not reach B (3 marks)

(b) 3.63 Ns (4 marks)

mr m. how did you work out 3(i)

Reply 65

Mr M

OP

Study Forum Helper

20

Original post by student.kid21

mr m. how did you work out 3(i)

T \cos 20 = 0.25 \times 9.8 \times \sin 30

Reply 66

student.kid21

Original post by Mr M

T \cos 20 = 0.25 \times 9.8 \times \sin 30

thanks what about 3(iii)

Reply 67

simple jackk

How did you do 7 b & 5 iii and are these answers 100%

Reply 68

JordanSadler2012

For the first question I completely misread it and thought the force of bearing 270 was 15N but then did all the resolving, Pythagoras and trig correct for 15N instead of 5N how many marks do you think I'd lose? Just 2 for the accuracy marks as I obviously got the wrong bearing and magnitude?

Reply 69

ActaNonVerba

Original post by simple jackk

How did you do 7 b & 5 iii and are these answers 100%

5iii) it's 0.2m in the air initially, it moves 0.2m up (same as the other particle because the string is taut) then use suvat to calculate the extra height it travels when the string is not taut, which is 0.1.. So 0.2+0.2+0.1=0.5m.. 7b has been explained multiple times in this thread, look at previous pages... And yeah these are 100%, but he didn't go into detail into what the marks are given for. Method marks

(edited 11 years ago)

Reply 70

saberahmed786

13

Original post by Mr M

Mr M's OCR (not OCR MEI) Mechanics 1 Answers January 2013

6(ii) (a) Q is in motion with a velocity of 1 m/s (4 marks)
(b) 2 seconds (4 marks)

Mr M. (or anyone for that matter) for question 6iia I wasn't sure which particle stopped so I wrote (literally): "if Q comes to rest then velocity of P is 2/3 m/s, if P comes to rest Q has a veolicty of 1 m/s"

the same went for part b, How many marks shall I expect to lose for such an error?

Reply 71

student.kid21

Original post by saberahmed786

Mr M. (or anyone for that matter) for question 6iia I wasn't sure which particle stopped so I wrote (literally): "if Q comes to rest then velocity of P is 2/3 m/s, if P comes to rest Q has a veolicty of 1 m/s"

the same went for part b, How many marks shall I expect to lose for such an error?

i couldnt understand how to work out the very same answer so i just guessed and got it right :colone:

Nevertheless I am also curious how we were meant to work this out

Reply 72

student.kid21

Original post by Mr M

You needed to work out v = 4.078 m/s then change in momentum = 0.4(5 + 4.078).

how would you work out v in the first place???

Reply 73

Tommmmmmmmm

You could work it out by first picking one randomly and saying it was in motion and the other was stationary. If you picked the wrong one and picked P was in motion and Q was stationary when you worked it out the only situation that could arise was that P would be traveling towards Q which is impossible because it would mean another collision took place. If you picked the right one to be in motion (Q) and said that P was stationary it worked out that Q was traveling away from P which was the only situation possible.

Reply 74

ActaNonVerba

Original post by student.kid21

how would you work out v in the first place???

This is for velocity, when the particle is coming down the plane..remember in part 7iia) you had to prove that it doesn't reach B (hence the distance travelled), it comes to rest because of friction acting on it (u=O), and you can work out acceleration using F=ma, then you use suvat to get V

Reply 75

Lilhazzaman

7

Couple of things im confused about...?
5)
iii) I put 0.3m (because I'm and idiot!), BUT did put at the top of the question to remind myself " This particle starts at 0.2m". How many marks will i gain out of 4! :frown:

6)
ii)
b) I couldnt remember the correct method of calculating the times for each to hit, so i used trial and error :smile:

Got the correct answer? Is this all four marks?
7)
ii)
b) Quite simply didnt have the time to do it; but managed to chuck down 2Ns for one of the occasions. One mark?

Reply 76

ActaNonVerba

Original post by Lilhazzaman

Couple of things im confused about...?
5)
iii) I put 0.3m (because I'm and idiot!), BUT did put at the top of the question to remind myself " This particle starts at 0.2m". How many marks will i gain out of 4! :frown:

6)
ii)
b) I couldnt remember the correct method of calculating the times for each to hit, so i used trial and error :smile:

Got the correct answer? Is this all four marks?
7)
ii)
b) Quite simply didnt have the time to do it; but managed to chuck down 2Ns for one of the occasions. One mark?

5iii) I think you'd lose 2. 6iib) it's time consuming for you, but I don't think you'll be penalised. 7iib) I hope that's a mark too :P, I did the change in momentum for when A is above B an vice versa.. Didn't read it properly but I had 2Ns written down

Reply 77

kinhew93

Original post by Lilhazzaman

Couple of things im confused about...?
5)
iii) I put 0.3m (because I'm and idiot!), BUT did put at the top of the question to remind myself " This particle starts at 0.2m". How many marks will i gain out of 4! :frown:

I did the exact same thing... *face palm*

Reply 78

waheed786

What does everyone reckon the approximate grade boundaries will be like for an A (Raw marks) ?.. i know its based on how well everyone else did, but regardless what do you think it will roughly be for an A out of 72 considering it was quite an easy paper compared to previous years. i think it will be about 60/72?..

Reply 79

Cyclohexane

Original post by waheed786

What does everyone reckon the approximate grade boundaries will be like for an A (Raw marks) ?.. i know its based on how well everyone else did, but regardless what do you think it will roughly be for an A out of 72 considering it was quite an easy paper compared to previous years. i think it will be about 60/72?..

I'd be inclined to agree. I think that many will have forgotten to take into account the original height on the pulley question, and friction for the momentum change of the last question, as well as Q6 being generally difficult (at least for a momentum question)!

I'd say high fifties for an A, probably 58/59.

Mr M's OCR (not OCR MEI) Mechanics 1 Answers January 2013

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