## Machines B/C

Umaroth
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### Re: Machines B/C

PandaShoelaces wrote:
February 11th, 2020, 10:09 am
How does one go about solving problem 11 from compound machines? It seems like there's an extra unknown variable all the time.
Which test are you referring to?
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### Re: Machines B/C

Umaroth wrote:
February 11th, 2020, 12:03 pm
PandaShoelaces wrote:
February 11th, 2020, 10:09 am
How does one go about solving problem 11 from compound machines? It seems like there's an extra unknown variable all the time.
Which test are you referring to?
I'm referring to the Compound Machines test from the 2020 SSSS on the test exchange.

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### Re: Machines B/C

KE=.5mv^2
PE = mgh
mgh = .5mv^2
10h=12.5
h=1.25

IMA = L/h
L=10
IMA = 10/1.25
IMA = 8
(Using conservation of energy)
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### Re: Machines B/C

what kinda string do ppl use to make their knots out of so they dont slip easily?
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### Re: Machines B/C

Most people just use fishing line - maybe use a bowline or some other knot to secure it.
If you want, you can use twine if you find it hard tying bowlines as simpler knots will do the trick there.
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### Re: Machines B/C

How do you calculate the AMA of an inclined plane if you are given the coefficient of kinetic friction and the length of the hypotenuse and height of the ramp? Thanks!

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### Re: Machines B/C

as1092 wrote:
February 18th, 2020, 7:42 pm
How do you calculate the AMA of an inclined plane if you are given the coefficient of kinetic friction and the length of the hypotenuse and height of the ramp? Thanks!
Someone correct me if this is wrong, but I'm pretty sure it's $AMA = \mu \frac{d_i}{d_v}$, or the coefficient of friction times the length of the hypotenuse over the height.
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### Re: Machines B/C

Hey guys, I was wondering what method you guys use to help get the mass ratio. I have started to practice using the lever, but I haven't been able to get a satisfactory time. Any help would be appreciated.
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### Re: Machines B/C

Vortexx2 wrote:
February 11th, 2020, 7:50 am
Unome wrote:
February 3rd, 2020, 1:20 pm
jaggie34 wrote:
February 3rd, 2020, 7:25 am

Last time machines was a nats event, top score was about 98.1, so I'd expect about 44 as the top device score
The scoring formula weights time more heavily this year iirc. I would not expect more than exceptional teams to be below 30 seconds in B and 40 seconds in C (with effectively perfect ratio scores of course).
I would have to disagree. I do it in around 40 seconds but thats also me going pretty slow. I could definitely see teams getting sub 30 seconds (div c) and still getting perfect ratio scores.
Is your machine built to have one mass fixed permanently? Because my design right now has a fixed place for the lighter mass, but I think it would be more efficient to have mass B fixed permanently, so I take on average 1:30 for time, with 29+ ratio score. Any help would be appreciated. Like how did you build your device bc 40 seconds seems close to impossible for me.

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### Re: Machines B/C

Does anyone know what the IMA of the following pulley is? https://drive.google.com/file/d/1ZzM_6W ... sp=sharing. The answer key says it's 6, but don't you multiply the IMA's to get 8? This is from the UT Invitational this year. Thanks!

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