You are Here: Home >< Maths

# Mechanics 2 question?!!

Announcements Posted on
Last day to win £100 of Amazon vouchers - don't miss out! Take our quick survey to enter 24-10-2016
1. Could someone help me with this please? I though it was Tcos60-5cos30=0.3g but the mark scheme says 5cos30=0.3g+Tcos60. Why is this?
http://www.thestudentroom.co.uk/atta...3&d=1459807059
2. If you resolve vertically there is only the component of tension of AP acting upwards. The forces acting downwards are the weight and the vertical component of the tension in the string PB. We assume P is in equilibrium, so the upwards forces must equal the downwards forces.
3. (Original post by Vanilla Poison)
If you resolve vertically there is only the component of tension of AP acting upwards. The forces acting downwards are the weight and the vertical component of the tension in the string PB. We assume P is in equilibrium, so the upwards forces must equal the downwards forces.
For similar questions I used the equation I thought and I got the answers write, e.g.Attachment 519875519877is this there something different about the question?
Attached Images

4. I don't know if you've got it right, but your first equation by resolving doesn't make any sense. It looks as though you're taking the forces acting down as positive (weight), but then the component of T2 is acting upwards. You'd realise this mistake if you brought all the forces to one side.
5. (Original post by Vanilla Poison)
I don't know if you've got it right, but your first equation by resolving doesn't make any sense. It looks as though you're taking the forces acting down as positive (weight), but then the component of T2 is acting upwards. You'd realise this mistake if you brought all the forces to one side.
It was a past paper question and the mark scheme said it was right and my teacher showed me the first equation, I don't know why it doesn't work for this question
6. Bump
7. (Original post by swagmister)
It was a past paper question and the mark scheme said it was right and my teacher showed me the first equation, I don't know why it doesn't work for this question
Can you clarify the issue? Perhaps post a link to the markscheme?
8. (Original post by swagmister)
Could someone help me with this please? I though it was Tcos60-5cos30=0.3g but the mark scheme says 5cos30=0.3g+Tcos60. Why is this?
http://www.thestudentroom.co.uk/atta...3&d=1459807059
Can u explain why u think ur ans is right ?
try resolving upwards, and remember gravity acts downwards
9. (Original post by Zacken)
Can you clarify the issue? Perhaps post a link to the markscheme?
http://www.ocr.org.uk/Images/62961-mark-scheme-june.pdf
Mechanics 2 question 6i for the second question I posted, I got question right, this is how I thought you work out the tension however for the first question I posted the mark scheme shows a different way which meant I got this question wrong.
Qusetion 6i http://www.ocr.org.uk/Images/62955-mark-scheme-june.pdf
I don't understand why they worked out the tension differently for the first question.
10. (Original post by Duke Glacia)
Can u explain why u think ur ans is right ?
try resolving upwards, and remember gravity acts downwards
I thought the vertical components of the tensions should be equal to the weight
11. (Original post by swagmister)
Could someone help me with this please? I though it was Tcos60-5cos30=0.3g but the mark scheme says 5cos30=0.3g+Tcos60. Why is this?
http://www.thestudentroom.co.uk/atta...3&d=1459807059
You seem to be saying that Tcos 60 acts in the opposite direction to weight? Why do you think this?
12. (Original post by Zacken)
You seem to be saying that Tcos 60 acts in the opposite direction to weight? Why do you think this?
Yep because its vertical component is up and I've treated up as negative and down as positive
13. (Original post by Zacken)
You seem to be saying that Tcos 60 acts in the opposite direction to weight? Why do you think this?
I just realised this is for the first question I posted, for that one I thought 5cos30 was in the opposite direction to the weight and Tcos60 was in the same direction as the weight
14. (Original post by swagmister)
Yep because its vertical component is up and I've treated up and negative and down as positive
The (vertical component of) tension in the string BP acts upwards and the (vertical component of) tension in the string AP acts upwards. So why do they have opposite signs in your equation?
15. (Original post by Zacken)
The (vertical component of) tension in the string BP acts upwards and the (vertical component of) tension in the string AP acts upwards. So why do they have opposite signs in your equation?
I thought Tcos60 (BP) was downwards and 5cos30 (AP) was upwards?
16. (Original post by swagmister)
I thought Tcos60 (BP) was downwards and 5cos30 (AP) was upwards?
Urgh, sorry. Craning my neck isn't helping. Apologies.
17. (Original post by swagmister)
I thought Tcos60 (BP) was downwards and 5cos30 (AP) was upwards?
5 cos 30 acts upwards. (AP)

T cos 60 acts downards. (BP)

Weight acts downards.

Upwards = downwards.

5 cos 30 = T cos 60 + weight

Your equation should be -5 cos 30 + T cos 60 + 3g = 0
18. (Original post by Zacken)
5 cos 30 acts upwards. (AP)

T cos 60 acts downards. (BP)

Weight acts downards.

Upwards = downwards.

5 cos 30 = T cos 60 + weight
How come this wasn't the case for the second question I posted?
19. (Original post by swagmister)
How come this wasn't the case for the second question I posted?
It is the case.

AP acts upwards. (T cos 60)

BP acts downwards (S cos 60)

Weight acts downwards.

Upwards = downwards

T cos 60 = S cos 60 + weight
20. (Original post by Zacken)
It is the case.

AP acts upwards. (T cos 60)

BP acts downwards (S cos 60)

Weight acts downwards.

Upwards = downwards

T cos 60 = S cos 60 + weight
Ah right the way I did it must have just worked for the second question because both the tensions were cos60? Thanks for helping

## Register

Thanks for posting! You just need to create an account in order to submit the post
1. this can't be left blank
2. this can't be left blank
3. this can't be left blank

6 characters or longer with both numbers and letters is safer

4. this can't be left empty
1. Oops, you need to agree to our Ts&Cs to register

Updated: April 10, 2016
TSR Support Team

We have a brilliant team of more than 60 Support Team members looking after discussions on The Student Room, helping to make it a fun, safe and useful place to hang out.

This forum is supported by:
Today on TSR

### How does exam reform affect you?

From GCSE to A level, it's all changing

Poll
Useful resources

### Maths Forum posting guidelines

Not sure where to post? Read here first

### How to use LaTex

Writing equations the easy way

### Study habits of A* students

Top tips from students who have already aced their exams

## Groups associated with this forum:

View associated groups
Study resources

The Student Room, Get Revising and Marked by Teachers are trading names of The Student Room Group Ltd.

Register Number: 04666380 (England and Wales), VAT No. 806 8067 22 Registered Office: International House, Queens Road, Brighton, BN1 3XE

Reputation gems: You get these gems as you gain rep from other members for making good contributions and giving helpful advice.