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# I need help on a mechanics 2 question watch

1. Which part? What have you tried?
2. Which part? What have you tried?

It will be useful if you post all your working and show us the diagram that you have drawn.

EDIT: RDKGames snap!
3. I have done part a and got acceleration to be 4.48ms^-2
Need help on part b
4. The string breaks so there's no tension anymore.

Now, consider the work done by the friction and the loss of mechanical energy
5. (Original post by shahs341)
I have done part a and got acceleration to be 4.48ms^-2
Need help on part b
It's very important that you tell us what you have tried and why you are stuck. This is a topic that is taught differently by different teachers so we need to know how you normally go about a question like this. If you post your working then that will show us.
6. My working out:

The diagram I used:

Part a working out: https://www.thestudentroom.co.uk/att...1&d=1483978356

attempt at b working out: https://www.thestudentroom.co.uk/att...1&d=1483978400
Attached Images

7. (Original post by shahs341)
My working out:

The diagram I used:
I haven't checked all your working but I think you've made a mistake when considering the gravitational potential energy.

Remember that the gain in GPE is equal to where is the vertical distance moved. But you need to work out the distance moved up the slope.

Does that help?
8. (Original post by shahs341)
My working out:

The diagram I used:

Part a working out: https://www.thestudentroom.co.uk/att...1&d=1483978356

attempt at b working out: https://www.thestudentroom.co.uk/att...1&d=1483978400
You need to also consider the work done by friction
9. When B descend down by 1m, does A also move 1m up the slope?
10. (Original post by metrize)
You need to also consider the work done by friction
K.E lost = mgh gained - work done by the frictional force ?
11. (Original post by notnek)
I haven't checked all your working but I think you've made a mistake when considering the gravitational potential energy.

Remember that the gain in GPE is equal to where is the vertical distance moved. But you need to work out the distance moved up the slope.

Does that help?
no sorry tried this and didn't get the right answer
12. (Original post by shahs341)
When B descend down by 1m, does A also move 1m up the slope?

yeah thats right
(Original post by shahs341)
K.E lost = mgh gained - work done by the frictional force ?
I got taught loss GPE + loss KE = work done by friction

I can try to answer it if you give me 5 mins, do you have the answer with you?
13. (Original post by shahs341)
When B descend down by 1m, does A also move 1m up the slope?
Yes but is that 'h' in the formula mgh?
14. (Original post by metrize)
yeah thats right

I got taught loss GPE + loss KE = work done by friction

I can try to answer it if you give me 5 mins, do you have the answer with you?
the answer from the book is 1.51 m

good luck!
15. (Original post by Muttley79)
Yes but is that 'h' in the formula mgh?
yes that's h - the vertical distance moved
16. (Original post by shahs341)
yes that's h - the vertical distance moved
1 metre up the slope is not 1 metre vertically ...
17. Here's what I did, see if you can follow it and get the answer:

Starting from Loss KE + Loss GPE = Work done by friction

I let d be the distance it moves up the slope. Since I let d be the distance up the slope, my loss in GPE will be negative
Work done by friction is d mu R.

Remember that the vertical height the object moves if it goes d up the slope is dsin theta vertically
18. (Original post by metrize)
Here's what I did, see if you can follow it and get the answer:

Starting from Loss KE + Loss GPE = Work done by friction

I let d be the distance it moves up the slope. Since I let d be the distance up the slope, my loss in GPE will be negative
Work done by friction is d mu R.

Remember that the vertical height the object moves if it goes d up the slope is dsin theta vertically
Well explained, I got the answer thanks!

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