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### Re: Simple Machines B/Compound Machines C

Posted: April 19th, 2015, 12:14 pm
UTF-8 U+6211 U+662F wrote:
Unome wrote:
Giant Mole Squad wrote:Does anyone know how to solve number 4 on the Captain's Tryouts test for Compound Machines?
Yeah, I spent so much time trying to figure out that one (and I still don't know); I never understood tension beyond what I needed to solve Div B level problems.
I think some free body diagrams would help here.

EDIT: I believe it's solved like this: $\Sigma F = ma \\* m_1 g - T = m_1 a \\* 2T - m_2 g = m_2 a \\* 2T = m_2 g + m_2 a \\* T = \frac{m_2 g + m_2 a}{2} \\* \frac{m_2 g - m_2 a}{2} - m_1 g = m_1 a \\* a = \frac{\frac{m_2 g - m_2 a}{2} - m_1 g}{m_1} \\* a = \frac{m_2 g - m_2 a - 2m_1 g}{2m_1}$
for first mass, and then just do the same thing for the other masses.
Hmm, the key says something different.

As of right now, I am only able to solve for the acceleration of their masses given their tension and mass, and I'm not really sure if I'm right.

### Re: Simple Machines B/Compound Machines C

Posted: April 19th, 2015, 7:18 pm
"Prohibited topics include: dynamic calculations"
Idk why everyone's trying so hard on that problem when it's never going to come up at nationals or anything .__.

### Re: Simple Machines B/Compound Machines C

Posted: April 19th, 2015, 11:00 pm
Where did the test go?

### Re: Simple Machines B/Compound Machines C

Posted: April 20th, 2015, 4:24 am
jkang wrote:"Prohibited topics include: dynamic calculations"
Idk why everyone's trying so hard on that problem when it's never going to come up at nationals or anything .__.
I was never quite sure what dynamic calculations were; is it just anything not in static equilibrium?

### Re: Simple Machines B/Compound Machines C

Posted: April 20th, 2015, 8:42 am
Unome wrote:
jkang wrote:"Prohibited topics include: dynamic calculations"
Idk why everyone's trying so hard on that problem when it's never going to come up at nationals or anything .__.
I was never quite sure what dynamic calculations were; is it just anything not in static equilibrium?
Essentially, yes, anything that involves calculating forces and whatnot related to bodies in motion is not allowed. At least that's my interpretation of the rules.

### Re: Simple Machines B/Compound Machines C

Posted: April 20th, 2015, 12:12 pm
Scio5ever wrote:
Unome wrote:
jkang wrote:"Prohibited topics include: dynamic calculations"
Idk why everyone's trying so hard on that problem when it's never going to come up at nationals or anything .__.
I was never quite sure what dynamic calculations were; is it just anything not in static equilibrium?
Essentially, yes, anything that involves calculating forces and whatnot related to bodies in motion is not allowed. At least that's my interpretation of the rules.
Err, no. That's allowed. Those problems are called net force problems.

### Re: Simple Machines B/Compound Machines C

Posted: April 20th, 2015, 3:11 pm
Unome wrote:
jkang wrote:"Prohibited topics include: dynamic calculations"
Idk why everyone's trying so hard on that problem when it's never going to come up at nationals or anything .__.
I was never quite sure what dynamic calculations were; is it just anything not in static equilibrium?
I would think so; the opposite of dynamic calculations should be static calculations, which would be anything in equilibrium. However I find it hard to believe that some basic dynamic calculations won't be included, for example the acceleration of masses on a fixed pulley would be something I would expect to come across at Nationals.

### Re: Simple Machines B/Compound Machines C

Posted: April 20th, 2015, 3:25 pm
RontgensWallaby wrote:
Unome wrote:
jkang wrote:"Prohibited topics include: dynamic calculations"
Idk why everyone's trying so hard on that problem when it's never going to come up at nationals or anything .__.
I was never quite sure what dynamic calculations were; is it just anything not in static equilibrium?
I would think so; the opposite of dynamic calculations should be static calculations, which would be anything in equilibrium. However I find it hard to believe that some basic dynamic calculations won't be included, for example the acceleration of masses on a fixed pulley would be something I would expect to come across at Nationals.
Of course, you can ask questions about forces... it's just that $\Sigma F$ has to equal zero.

### Re: Simple Machines B/Compound Machines C

Posted: April 21st, 2015, 6:43 pm
http://img.sparknotes.com/content/testp ... pulley.gif
A problem I just came up with. Solved it and just want to make sure I'm right since I doubt my coach will know how to solve it (it's not that complicated).
In the diagram from the link, angle θ is 37 degrees and mass m is 15 kg. The coefficient of friction between mass m and the inclined plane is 0.4. Assume the pulley is frictionless. What are the maximum and minimum masses for mass M if the system is in equilibrium?

### Re: Simple Machines B/Compound Machines C

Posted: April 21st, 2015, 7:15 pm
RontgensWallaby wrote:http://img.sparknotes.com/content/testp ... pulley.gif
A problem I just came up with. Solved it and just want to make sure I'm right since I doubt my coach will know how to solve it (it's not that complicated).
In the diagram from the link, angle θ is 37 degrees and mass m is 15 kg. The coefficient of friction between mass m and the inclined plane is 0.4. Assume the pulley is frictionless. What are the maximum and minimum masses for mass M if the system is in equilibrium?
I got 4.235 kg <= M <= 13.82 kg? Got 4.235 kg by assuming left side was heavy, 13.82 by assuming right. With sig figs (mu only has one), 4 kg and 10 kg.