circular motion

help pls - thats the further mechanics 2 challenge from exercise 1a.

All i have got is that the ratio of the angular velocities is 10:9 (that's larger:smaller)

idk how to use the info about how after 10 seconds they r at their furthest points - like obviously they are both on the opposite side to where they started but how does that help?

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Reply 1

mqb2766

If the angular velocities are in the ratio 10:9, assume one part is "w". What is the relative velocity of one turntable and how far (relative angle) does it move in 10 s? Then solve for w.

(edited 1 year ago)

Reply 2

ligmaAss

Original post by mqb2766

If the angular velocities are in the ratio 10:9, assume one part is "w". What is the relative velocity of one turntable and how far (relative angle) does it move in 10 s? Then solve for w.

im sorry i dont see what you mean :frown:

Reply 3

mqb2766

Original post by ligmaAss

im sorry i dont see what you mean :frown:

Which part? If one turntable is rotating 10w anticlockwise and the other 9w clockwise, what is the relative speed of one compared to (a stationary) other? How far (relative, angular) does it need to move in 10s? Then just solve for w.

Reply 4

ligmaAss

Original post by mqb2766

what is w here? because i have one as w1, and the other as w2, hence 10w1=9w2

Reply 5

mqb2766

Original post by ligmaAss

what is w here? because i have one as w1, and the other as w2, hence 10w1=9w2

You did ratios in ~y5? Maybe a quick review is needed.

(edited 1 year ago)

Reply 6

ligmaAss

Original post by mqb2766

You did ratios in ~y5? Maybe a quick review is needed.

lololol; you said "assume one part is w" - like what does that even mean

Reply 7

mqb2766

Original post by ligmaAss

lololol; you said "assume one part is w" - like what does that even mean

https://www.youtube.com/watch?v=7PFniZ8XoQ0&ab_channel=MathwithMr.J
https://www.bbc.co.uk/bitesize/guides/zpxyrwx/revision/1

(edited 1 year ago)

Reply 8

ligmaAss

Original post by mqb2766

https://www.bbc.co.uk/bitesize/topics/zsq7hyc/articles/z8kfnbk
https://www.bbc.co.uk/bitesize/guides/zpxyrwx/revision/1

i have literally no idea what you are saying when you say "one part is w" - obviously i know how ratios work there is no need to be so annoying

Reply 9

mqb2766

Original post by ligmaAss

i have literally no idea what you are saying when you say "one part is w" - obviously i know how ratios work there is no need to be so annoying

Using your view of ratios, what is the speed of either hand in terms of the other and what is then the relative speed. Its easier (avoids fractions) if you do it as parts.

Reply 10

ligmaAss

Original post by mqb2766

Using your view of ratios, what is the speed of either hand in terms of the other and what is then the relative speed. Its easier (avoids fractions) if you do it as parts.

ok right so the relative speed is w - omg i understand what you mean. But after 10 seconds, you don't know how many revolutions have occured :/

Reply 11

mqb2766

Original post by ligmaAss

ok right so the relative speed is w - omg i understand what you mean. But after 10 seconds, you don't know how many revolutions have occured :/

After 10s they are furthest apart for the first time.
Not sure the relative speed is w as they're moving in opposite direcdtions, but the usual advice is that a sketch helps.

Reply 12

ligmaAss

Original post by mqb2766

After 10s they are furthest apart for the first time.
Not sure the relative speed is w as they're moving in opposite direcdtions, but the usual advice is that a sketch helps.

ive drawn a sketch and am still lost like actually - i might just give up

Reply 13

mqb2766

Original post by ligmaAss

ive drawn a sketch and am still lost like actually - i might just give up

What does your sketch look like?

Original post by ligmaAss

There isnt a huge amount to go on there. But If you imagined the blue turntable as fixed, what would be the relative speed of the red one, how far would it have rotated in 10s? Rather than talking about relative speed, you could talk about speed of seperation as it would be equivalent.

Reply 16

ligmaAss

Original post by mqb2766

if the blue one is fixed, then the speed of the red one is 19w, and after 10 seconds i'm not sure how far it has moved - i swear there is no info about this

Reply 17

ghostwalker

Red Alert: (OK, just been watching Star Trek)

That diagram is incorrect. According to the question they have a common vertical axis, and are mounted horizontally.

(edited 1 year ago)

Reply 18

mqb2766

Original post by ligmaAss

if the blue one is fixed, then the speed of the red one is 19w, and after 10 seconds i'm not sure how far it has moved - i swear there is no info about this

In your diagram, youre starting at different locations. If they both started at teh same point (say 12 o clock) and you imagine the blue one fixed, how far would the red one have rotated when its as far frmo the blue one as possible.

Reply 19

ligmaAss

Original post by ghostwalker

Red Alert: (OK, just been watching Star Trek)

That diagram is incorrect. According to the question they have a common vertical axis, and are mounted horizontally.