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- Thread starter Torater
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- #2

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∑fx=-m2a = Tsin30-m2gsin30

∑τ= Iα = Tr

T= m2(gsin30-a)/sin30

I=mr²

m1a=m2(gsin30-a)/sin30

sin30 (5 a)= (8 (9.81sin30)-a)

sin30 (5a) + 8a = 39.24

a= 6.04m/s²

T= (8)(9.81sin30-6.04)/sin30

T= -18.2N

- #3

tiny-tim

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Hi Torater!

uhh?sin30 (5a) + 8a = 39.24

a= 6.04m/s²

- #4

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r= .25m

m1=5kg

I=mr2

M=5+cos30(5)

mt=7.5 + 8

a= (8 (9.81)sin30/15.5

a= 2.53

m1=5kg

I=mr2

M=5+cos30(5)

mt=7.5 + 8

a= (8 (9.81)sin30/15.5

a= 2.53

Last edited:

- #5

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tiny tim i did my algebra wrong!! 3.74??

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tiny-tim

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- #7

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ok attempt 2 at shortcut:

pseudo mass: mr^2 / r^2 = 5

M = 5+5 = 10

a= (8(9.81) sin30/10

a= 3.92

Ok lets focus on the long way as its what the question asks I don't think I did that right again.... maybe...

Or is my long approach still not right, and if not where? lol I got to start studying other chapters

- #8

tiny-tim

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No, the effective mass is the whole of the 8 plus the whole of the 5, = 13 …M = 5+5 = 10

whyever did you add the 5 to itself?

(and your arithmetic in your "long approach" was wrong, so it's difficult to check the rest)

- #9

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Where did I go wrong so I can correct this.... Like are my sum of force equations right?

Did I substitute them into other equations wrong? Or is the fact that I didn't use the Y forces at all wrong?

please direct me....

Whoops i didn't catch the whole effective mass part of that shortcut,

so it should come out to M=13 therefore a--> 8(9.81sin30)/13 = 3.02

- #10

tiny-tim

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I showed you where, in post #3Where did I go wrong so I can correct this....

that's right!Whoops i didn't catch the whole effective mass part of that shortcut,

so it should come out to M=13 therefore a--> 8(9.81sin30)/13 = 3.02

(you really

- #11

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so then my tension should work out to 30.2..... haha lets hope I did this right

- #12

tiny-tim

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No … how did you get that?so then my tension should work out to 30.2

- #13

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T= 8(9.81sin30 - 3.02)

T= 15.1N?

Before I did this:

T=8(9.81sin30 - 3.02)/sin30

T= 15.1N?

Before I did this:

T=8(9.81sin30 - 3.02)/sin30

- #14

tiny-tim

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Yup!T= 8(9.81sin30 - 3.02)

T= 15.1N?

(using the short-cut, you could also have said it was 5 times 3.02 = 15.1 )

- #15

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Thank you so much for all your help, and putting up with my dumb errors throughout hahah

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