## Machines B/C

AwersomeUser
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### Re: Machines B/C

AlfWeg wrote:
September 26th, 2019, 5:26 pm
AwersomeUser wrote:
September 26th, 2019, 5:09 pm
Ah! Sorry, I forgot to hide my answer...

1) Most machines have an actual mechanical advantage of more less one. True/False
2) The following is an example of what kind of simple machines?

3) A boy and a girl each sits on one end of a seesaw. When the 120 kg girl sits down, the boy rises/goes up by 0.4 m; when the boy sits down, the girl rise/goes up by 20 cm. How heavy is the boy in kilogram?
(Hope the wording isn’t too confusing)
I'll take a stab at it... 1) Most have more than one AMA
2) Belt and Pulley, or just 2 pulleys
3) 60KG? I'm more than a bit confused on this question, is this even possible?
Correct for one. I wouldn’t put belt too for two. The correct answer for 3 is 9.6 kg. I guess the
problem doesn’t make sense with a boy that weights 9.6 kg. (Ugh... If someone’s 9.6 kg they are probably still a baby/toddler, not a boy...) I was going to make him weigh 96 kg... How did you get 60 kg? Maybe I am wrong.
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JoeyC
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### Re: Machines B/C

How did you get the answer in the first place? As far as I see the system would just oscillate until it stopped due to frictional forces... (I mean, not just from a physics standpoint, it's called a seesaw because when you get on it it goes up and down)
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### Re: Machines B/C

AwersomeUser wrote:
September 26th, 2019, 6:12 pm
AlfWeg wrote:
September 26th, 2019, 5:26 pm
AwersomeUser wrote:
September 26th, 2019, 5:09 pm
Ah! Sorry, I forgot to hide my answer...

1) Most machines have an actual mechanical advantage of more less one. True/False
2) The following is an example of what kind of simple machines?

3) A boy and a girl each sits on one end of a seesaw. When the 120 kg girl sits down, the boy rises/goes up by 0.4 m; when the boy sits down, the girl rise/goes up by 20 cm. How heavy is the boy in kilogram?
(Hope the wording isn’t too confusing)
I'll take a stab at it... 1) Most have more than one AMA
2) Belt and Pulley, or just 2 pulleys
3) 60KG? I'm more than a bit confused on this question, is this even possible?
Correct for one. I wouldn’t put belt too for two. The correct answer for 3 is 9.6 kg. I guess the
problem doesn’t make sense with a boy that weights 9.6 kg. (Ugh... If someone’s 9.6 kg they are probably still a baby/toddler, not a boy...) I was going to make him weigh 96 kg... How did you get 60 kg? Maybe I am wrong.
A boy weighing 96 kg would be rather concerning since average American adult males weigh around 90 kg.

AlfWeg
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### Re: Machines B/C

AwersomeUser wrote:
September 26th, 2019, 6:12 pm
AlfWeg wrote:
September 26th, 2019, 5:26 pm
AwersomeUser wrote:
September 26th, 2019, 5:09 pm
Ah! Sorry, I forgot to hide my answer...

1) Most machines have an actual mechanical advantage of more less one. True/False
2) The following is an example of what kind of simple machines?

3) A boy and a girl each sits on one end of a seesaw. When the 120 kg girl sits down, the boy rises/goes up by 0.4 m; when the boy sits down, the girl rise/goes up by 20 cm. How heavy is the boy in kilogram?
(Hope the wording isn’t too confusing)
I'll take a stab at it... 1) Most have more than one AMA
2) Belt and Pulley, or just 2 pulleys
3) 60KG? I'm more than a bit confused on this question, is this even possible?
Correct for one. I wouldn’t put belt too for two. The correct answer for 3 is 9.6 kg. I guess the
problem doesn’t make sense with a boy that weights 9.6 kg. (Ugh... If someone’s 9.6 kg they are probably still a baby/toddler, not a boy...) I was going to make him weigh 96 kg... How did you get 60 kg? Maybe I am wrong.
Would u mind explaining number 3? I always thought that was not possible...
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knightmoves
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### Re: Machines B/C

AlfWeg wrote:
September 27th, 2019, 4:31 am
Would u mind explaining number 3? I always thought that was not possible...
Yeah - that's not how seesaws work. If a boy and a girl sit on a seesaw, the heavier one falls down until his or her legs stop the motion. The height of the lighter one depends on the leg extension of the heavier one, and not on their relative weights.

AlfWeg
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### Re: Machines B/C

knightmoves wrote:
September 27th, 2019, 8:45 am
AlfWeg wrote:
September 27th, 2019, 4:31 am
Would u mind explaining number 3? I always thought that was not possible...
Yeah - that's not how seesaws work. If a boy and a girl sit on a seesaw, the heavier one falls down until his or her legs stop the motion. The height of the lighter one depends on the leg extension of the heavier one, and not on their relative weights.
Oh goodie I’m not crazy. But I’m just wondering how the Awersome got an answer. Maybe he meant length?
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AwersomeUser
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### Re: Machines B/C

knightmoves wrote:
September 27th, 2019, 8:45 am
AlfWeg wrote:
September 27th, 2019, 4:31 am
Would u mind explaining number 3? I always thought that was not possible...
Yeah - that's not how seesaws work. If a boy and a girl sit on a seesaw, the heavier one falls down until his or her legs stop the motion. The height of the lighter one depends on the leg extension of the heavier one, and not on their relative weights.
Yes, probably. Pretend I never posted that question.

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AlfWeg
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### Re: Machines B/C

Lol I make mistakes like that all the time

A 20 kg block is stationary on a inclined plane(20 degree angle). What is the coefficient of static friction? Use g= 9.81
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JoeyC
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### Re: Machines B/C

Fg=Fs
mgsin(theta)=umgcos(theta)
sin(theta)=ucos(theta)
u=sin(theta)/cos(theta)
u = tan(theta)
u = ~.364
Ohayo!
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AlfWeg
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### Re: Machines B/C

JoeyC wrote:
September 28th, 2019, 10:00 am
Fg=Fs
mgsin(theta)=umgcos(theta)
sin(theta)=ucos(theta)
u=sin(theta)/cos(theta)
u = tan(theta)
u = ~.364