Machines B/C

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Re: Machines B/C

Post by AwersomeUser »

AlfWeg wrote: Thu Sep 26, 2019 5:26 pm
AwersomeUser wrote: Thu Sep 26, 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?
Image
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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Re: Machines B/C

Post by JoeyC »

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

Post by UTF-8 U+6211 U+662F »

AwersomeUser wrote: Thu Sep 26, 2019 6:12 pm
AlfWeg wrote: Thu Sep 26, 2019 5:26 pm
AwersomeUser wrote: Thu Sep 26, 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?
Image
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.
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Re: Machines B/C

Post by AlfWeg »

AwersomeUser wrote: Thu Sep 26, 2019 6:12 pm
AlfWeg wrote: Thu Sep 26, 2019 5:26 pm
AwersomeUser wrote: Thu Sep 26, 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?
Image
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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Re: Machines B/C

Post by knightmoves »

AlfWeg wrote: Fri Sep 27, 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.
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Re: Machines B/C

Post by AlfWeg »

knightmoves wrote: Fri Sep 27, 2019 8:45 am
AlfWeg wrote: Fri Sep 27, 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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Re: Machines B/C

Post by AwersomeUser »

knightmoves wrote: Fri Sep 27, 2019 8:45 am
AlfWeg wrote: Fri Sep 27, 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.

Your turn AlfWeg.
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Re: Machines B/C

Post by AlfWeg »

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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Re: Machines B/C

Post by JoeyC »

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

Post by AlfWeg »

JoeyC wrote: Sat Sep 28, 2019 10:00 am Fg=Fs
mgsin(theta)=umgcos(theta)
sin(theta)=ucos(theta)
u=sin(theta)/cos(theta)
u = tan(theta)
u = ~.364
Yup. Your turn!
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