# The cylinder moves downwards a distance x. How far up does the box move in that time?

Watch
Announcements

Page 1 of 1

Go to first unread

Skip to page:

Q (part a): http://prntscr.com/uephr4

I don't think there is a way to solve this question as I'm dealing with 3 unknowns: T2, x, & a. I tried using simultaneous equations but I end up with 6g = 0a.

My diagram: http://prntscr.com/uepq82

Since the box and the cylinder have the same acceleration they should both travel a distance of x if they're stop times are equal. So why is the distance for the box 2x?

I don't think there is a way to solve this question as I'm dealing with 3 unknowns: T2, x, & a. I tried using simultaneous equations but I end up with 6g = 0a.

My diagram: http://prntscr.com/uepq82

Since the box and the cylinder have the same acceleration they should both travel a distance of x if they're stop times are equal. So why is the distance for the box 2x?

Last edited by TSR360; 2 months ago

0

reply

Report

#2

It should be a simple string length question. No forces are needed.

The string length is constant, if the left part and middle parts are longer (how much?), how much shorter is the right part?

edit - they don't have the same acceleration.

The string length is constant, if the left part and middle parts are longer (how much?), how much shorter is the right part?

edit - they don't have the same acceleration.

Last edited by mqb2766; 2 months ago

0

reply

(Original post by

It should be a simple string length question. No forces are needed.

The string length is constant, if the left part and middle parts are longer (how much?), how much shorter is the right part?

edit - they don't have the same acceleration.

**mqb2766**)It should be a simple string length question. No forces are needed.

The string length is constant, if the left part and middle parts are longer (how much?), how much shorter is the right part?

edit - they don't have the same acceleration.

0

reply

Report

#4

**mqb2766**)

It should be a simple string length question. No forces are needed.

The string length is constant, if the left part and middle parts are longer (how much?), how much shorter is the right part?

edit - they don't have the same acceleration.

I can see where the 2x distance has come from, but can I just check - is the OP's diagram correct apart from the assumption that the accelerations are equal?

So our assumption in solving this is that the tape's tension is constant throughout, and without further information we can only write the box's acceleration and the overall tension in terms of a. Am I thinking this out correctly?

0

reply

Report

#5

(Original post by

I'm not the OP and not looking for a solution, but this looks interesting as it's a bit trickier than the usual "two objects hanging over a pulley" questions!

I can see where the 2x distance has come from, but can I just check - is the OP's diagram correct apart from the assumption that the accelerations are equal?

So our assumption in solving this is that the tape's tension is constant throughout, and without further information we can only write the box's acceleration and the overall tension in terms of a. Am I thinking this out correctly?

**davros**)I'm not the OP and not looking for a solution, but this looks interesting as it's a bit trickier than the usual "two objects hanging over a pulley" questions!

I can see where the 2x distance has come from, but can I just check - is the OP's diagram correct apart from the assumption that the accelerations are equal?

So our assumption in solving this is that the tape's tension is constant throughout, and without further information we can only write the box's acceleration and the overall tension in terms of a. Am I thinking this out correctly?

Parts b&c bring tensions and accelerations into the probkem. It's not needed for a). Part c) says the tape tension is constant throughout?

Obviously this is the basis for pulleys, where the work is

Force*distance

So you use a pulley to apply a higher force over a shorter distance for the same work done. See pulley - mechanical advantage examples in

https://www.bbc.co.uk/bitesize/guide...6yc/revision/6

Last edited by mqb2766; 2 months ago

0

reply

Report

#6

One of these days we might even get a block and tackle question on here - unless they're all in physics help.

0

reply

Report

#7

This is a (simple, rearranged) gun tackle

https://en.m.wikipedia.org/wiki/Block_and_tackle

https://en.m.wikipedia.org/wiki/Block_and_tackle

0

reply

Report

#8

(Original post by

Part c) says the tape tension is constant throughout?

**mqb2766**)Part c) says the tape tension is constant throughout?

(Original post by

One of these days we might even get a block and tackle question on here - unless they're all in physics help.

**ghostwalker**)One of these days we might even get a block and tackle question on here - unless they're all in physics help.

0

reply

Report

#9

(Original post by

As memory serves, "smooth pulley" is the magic phrase that says "you can assume the tension is constant along the string".

I thought Step I, 2014, Q11 was quite a fun pulley question.

**DFranklin**)As memory serves, "smooth pulley" is the magic phrase that says "you can assume the tension is constant along the string".

I thought Step I, 2014, Q11 was quite a fun pulley question.

0

reply

(Original post by

The left object goes down by x. The left and middle substring must be x longer each. To the OP, you need differences, not proportions. They rob this from the right substring which must be 2x shorter.

Parts b&c bring tensions and accelerations into the probkem. It's not needed for a). Part c) says the tape tension is constant throughout?

Obviously this is the basis for pulleys, where the work is

Force*distance

So you use a pulley to apply a higher force over a shorter distance for the same work done. See pulley - mechanical advantage examples in

https://www.bbc.co.uk/bitesize/guide...6yc/revision/6

**mqb2766**)The left object goes down by x. The left and middle substring must be x longer each. To the OP, you need differences, not proportions. They rob this from the right substring which must be 2x shorter.

Parts b&c bring tensions and accelerations into the probkem. It's not needed for a). Part c) says the tape tension is constant throughout?

Obviously this is the basis for pulleys, where the work is

Force*distance

So you use a pulley to apply a higher force over a shorter distance for the same work done. See pulley - mechanical advantage examples in

https://www.bbc.co.uk/bitesize/guide...6yc/revision/6

0

reply

Report

#11

(Original post by

This info on pulleys wasn't covered at all in my textbook. Is it common knowledge or are they assuming I study physics?

**TSR360**)This info on pulleys wasn't covered at all in my textbook. Is it common knowledge or are they assuming I study physics?

Tbh, it's the simplest such pulley and it's not unreasonable that you could apply the stuff you learnt on a level mechanics to a simple gcse-type problem. The question tries to walk you through the approach by getting you to think about distances, then accelerations, then tension. Rather than the other way round. So a bit unusual but not unreasonable.

0

reply

(Original post by

That link was to gcse physics.

Tbh, it's the simplest such pulley and it's not unreasonable that you could apply the stuff you learnt on a level mechanics to a simple gcse-type problem. The question tries to walk you through the approach by getting you to think about distances, then accelerations, then tension. Rather than the other way round. So a bit unusual but not unreasonable.

**mqb2766**)That link was to gcse physics.

Tbh, it's the simplest such pulley and it's not unreasonable that you could apply the stuff you learnt on a level mechanics to a simple gcse-type problem. The question tries to walk you through the approach by getting you to think about distances, then accelerations, then tension. Rather than the other way round. So a bit unusual but not unreasonable.

0

reply

Report

#13

(Original post by

I don't remember covering pulleys in that much depth in my GCSEs. I looked up the word in my old Edexcel CGP physics textbook and it only appears 5 or 6 times in total. The link you provided is for the AQA GCSE spec, so maybe that is why? Looks like I need to get the AQA CGP textbook now...lol

**TSR360**)I don't remember covering pulleys in that much depth in my GCSEs. I looked up the word in my old Edexcel CGP physics textbook and it only appears 5 or 6 times in total. The link you provided is for the AQA GCSE spec, so maybe that is why? Looks like I need to get the AQA CGP textbook now...lol

Last edited by mqb2766; 2 months ago

0

reply

X

Page 1 of 1

Go to first unread

Skip to page:

### Quick Reply

Back

to top

to top