# M3 verticle circle inequality condition

Watch
Announcements
#1
bit confused, it is that T (or R or V) has to be equal to or greater than 0, or just greater than? (as the condition for a particle moving in a full circle)

originally thought it was the latter, but question 6 in M3 june 2016 uses the former

http://qualifications.pearson.com/co...s_20160817.pdf
(page 12/15)

any help appreciated
0
3 years ago
#2
By assuming that v>=0 at the top of the circle will enable the particle to complete a full circle would generate an incorrect inequality.

Thinking practically, if the radius of the circle is 500m, and the speed at the top of the circle is 0.1ms, it clearly won't continue to act in circular motion. The tension needs to be greater or equal to zero so the particle acts with circular motion

Posted from TSR Mobile
0
#3
(Original post by chemistryboi)
By assuming that v>=0 at the top of the circle will enable the particle to complete a full circle would generate an incorrect inequality.

Thinking practically, if the radius of the circle is 500m, and the speed at the top of the circle is 0.1ms, it clearly won't continue to act in circular motion. The tension needs to be greater or equal to zero so the particle acts with circular motion

Posted from TSR Mobile
yeah I guess that makes sense for velocity, but if you check the markscheme for the linked question it is T>=0?
0
3 years ago
#4
(Original post by the___jackal)
bit confused, it is that T (or R or V) has to be equal to or greater than 0, or just greater than? (as the condition for a particle moving in a full circle)

originally thought it was the latter, but question 6 in M3 june 2016 uses the former

http://qualifications.pearson.com/co...s_20160817.pdf
(page 12/15)

any help appreciated
For vertical motion in a circle, where the mass is attached via a string, you require at all times.

There is only one instance of time when the tension could be zero, and that will be when the mass is vertically above the centre of motion; the remainder of the time it will be >0.

Think about it: If you had zero tension for any length of time, then you'd be moving freely under gravity, which is parabolic, not circular.
0
3 years ago
#5
(Original post by the___jackal)
bit confused, it is that T (or R or V) has to be equal to or greater than 0, or just greater than? (as the condition for a particle moving in a full circle)

originally thought it was the latter, but question 6 in M3 june 2016 uses the former

http://qualifications.pearson.com/co...s_20160817.pdf
(page 12/15)

any help appreciated
As Ghostwalker says, if the particle CAN fall out of its circle then we need T (or R) to be >=0.

If however the particle must stay in its circle, such as at the end of a rotating rod or threaded inside a circular tube, it is V that matters. V at the top must be strictly > 0. If V is 0 at the top, it will just stay there.
1
X

new posts
Back
to top
Latest
My Feed

### Oops, nobody has postedin the last few hours.

Why not re-start the conversation?

see more

### See more of what you like onThe Student Room

You can personalise what you see on TSR. Tell us a little about yourself to get started.

### Poll

Join the discussion

#### Should there be a new university admissions system that ditches predicted grades?

No, I think predicted grades should still be used to make offers (516)
33.68%
Yes, I like the idea of applying to uni after I received my grades (PQA) (634)
41.38%
Yes, I like the idea of receiving offers only after I receive my grades (PQO) (312)
20.37%
I think there is a better option than the ones suggested (let us know in the thread!) (70)
4.57%