# Ch 8_3 help

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## Re: Ch 8_3 help

All the formulas are there given. They all worked for me. I think a few were mislabeled, but just read your question and you'll see which ones.

Question 1:
(Positive)
a=(m*g)/((M/2)+m)

Question 2:
(Negative)
Here's the method:
L (angular momentum) = I (moment of inertia) * W (angular velocity).
therefore, I = (2/5) factor that was provided in the question * M (in Kg)* (R^2), R being in meters! and W = rpm given in the question * ((2*pi)/60) = (rads/seconds)
Multiply the I and W and you get your angular momentum:
Here is my problem and answer:
A uniform 2.728 kg sphere (the factor f=2/5 on sheet 1Cool with a 53.37 cm radius spins at 33.42 rpm. What is the angular momentum of the sphere (see sheet 26). Indicate with a negative (positive) sign whether the angular momentum stays the same (changes) in the absence of any torque acting on the sphere.
Ans: -1.087761858

THANKS MIT!

To break it down just multiply across, watch order of operations!
L=((2/5)*M*R2)*(RPM*((2pi)/60))

Question 3:
(Negative)
w=(I'w')/I
becomes...
w=(1/I*w)
The ratio is given, but it becomes one over (1/x), multiply it by the w.

Question 4:
(Negative)
(M*%[NOTE: in decimal form]*9.81*L)+(m*9.81)]/(Sin(x)*.45[NOTE: should be the same number, but it's the second L given])

Hope that helps. See you all in a few hours!

Guest01

Posts : 133
Join date : 2008-09-19

## #1

I got the formula for #1 from the posts, but I can not figure out how. Can someone post the breakdown of the formulas. I would really like to know.

super Mo
Guest

## simplified solution to all 4 questions

(m*g)/((M/2)+m)

where m=mass hanging and M=mass of the disk

(.4*m*(r^2))/(rpm*(2pi/60))

divide angular velocity w given by the value given for the ratio

((9.81*m)+(9.81*M*L1*(percent/100)))/(L2*(sin(theta)))

where m=weight held, M=mass of the person, L1=first L given, L2=second L given

hope this helps! any questions, get at me

izzy
Guest