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

Posted: **April 20th, 2015, 12:12 pm**

by **samlan16**

"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**

by **RontgensWallaby**

"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**

by **UTF-8 U+6211 U+662F**

"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

has to equal zero.

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

Posted: **April 21st, 2015, 6:43 pm**

by **RontgensWallaby**

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**

by **jkang**

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.

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

Posted: **April 22nd, 2015, 2:11 pm**

by **RontgensWallaby**

Ok, that's what I got.

(originally I solved incorrectly for the minimum mass and used the total weight of the block as the force it exerted, for some reason)

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

Posted: **April 22nd, 2015, 2:13 pm**

by **RontgensWallaby**

The only other thing was that my minimum mass was 4 grams heavier than yours but that shouldn't be an issue. Probably a result of different intermediate rounding.

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

Posted: **April 22nd, 2015, 3:31 pm**

by **UTF-8 U+6211 U+662F**

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?

Just want to make sure you know you don't have to know this. Div B prohibited topics include coefficient of friction.

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

Posted: **May 20th, 2015, 2:35 pm**

by **Unome**

Okay, so as far as I can tell, if the following system is in static equilibrium, the downward force on the fulcrum would be 16.82; I just wanted to check here and see if that makes sense:

- Lever 2nd class.png (3.61 KiB) Viewed 3561 times

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

Posted: **May 20th, 2015, 2:45 pm**

by **UTF-8 U+6211 U+662F**

Okay, so as far as I can tell, if the following system is in static equilibrium, the downward force on the fulcrum would be 16.82; I just wanted to check here and see if that makes sense:

Lever 2nd class.png

Strange... I got an upward force of 16.82 N (with sig figs that's 20 N).