Recent content by justagirl

  1. J

    Simple Compression question

    What am I doing wrong in this problem? You need to record an entire collection of your favorite music. It consists of 39 hours of music. Assuming you are using MP3 encoding (MPEG Audio Level III at about 128kb per second), how many CDs will you need? (hint: a CD can store up to 700 MB of...
  2. J

    HELP! Harmonic Motion

    Can you offer some help on the following question? I've been trying different things for a while but can't get the right answer. Thanks! At time t = 0, consider a 1/2 wavelength long section of the rope which is carrying the wave y = 0.06 cos(2.1 t - 2.4 x) between two points which have zero...
  3. J

    Radius of Gyration? REALLY need help

    Radius of Gyration? REALLY need help ASAP!!! Hey - :surprised If any of you can help me with the following problem asap that would be awesome!! A racquet consists of uniform lamina that occupies the region inside the right-hand loop of r^2 = cos 2theta on the end of a handle (assumed to...
  4. J

    HELP! Angular Acceleration

    Okay... treating them as point masses: alpha = torque / I = (m1)gr - (m2)gr / m1(r^2) + m2(r^2) = 12(9.8)(0.25) - 6(9.8)(0.25) / ((.25^2) (m1 + m2)) = 13.1 Is that right? So the position of the center of mass doesn't really matter in this case? Thanks!
  5. J

    HELP! Angular Acceleration

    A dumbbell consists of a slender rod of negligible mass and small spheres attached to each end with mass 12-kg and 6-kg respectively. It is pivoted at its center about a fixed horizontal frictionless axle and initially held in place horizontally. The length of the rod is 50 centimeters and...
  6. J

    If there is a net torque on a system does that mean there's net force on the system

    if there is a net torque on a system does that mean there must be a net force on the system
  7. J

    Mechanics PLEASE HELP VERY SOON

    Suppose now that I want to calculate the tangential force. I set torque = I(alpha) = F(R) F = I(alpha) / R = (1/3)ML^2*(a/R) / R F = (1/3)ML^2*((g sin_theta)/(L/2)) / (L/2) I got that F_tangential = 4/3Mgsin_theta, but they got that the answer is 1/4 Mg sin_theta. What did I do...
  8. J

    Mechanics PLEASE HELP VERY SOON

    thanks Everything did come together. Thank you for your help!
  9. J

    Mechanics PLEASE HELP VERY SOON

    Mechanics...PLEASE HELP VERY SOON!!! Can someone please help me with this problem? I've been working on it for hours - anything would help thanks! A system consists of a uniform stick of length L and mass M hinged at one end. The hinge is released from rest at an angle theta_0 with respect...
  10. J

    Rotational Motion

    help! can someone please answer/
  11. J

    Rotational Motion

    would the smaller inertia hoop be going faster or does it not matter? I think we did this experiment where we found acceleration to be g sin theta / (1 + c), where c was the constant of inertia. (i.e., 1/2 for a cylinder and 1 for a hoop).
  12. J

    Rotational Motion

    I'm a lil confused: so by conservation of energy I have: mgh = 1/2mv^2 + 1/2Iw^2 mgh = 1/2mv^2 + 1/2I(v^2/r^2) V^2(1/2m + 1/2(I/R^2) = mgh v^2 = mgh / (1/2m + 1/2(I/R^2)) For spoke one, the mass is greater, so speed decreases... But wouldn't I be smaller? Wouldn't that increase...
  13. J

    Rotational Motion

    re; The part of I'm confused on is this: The wheel with the spokes has more mass, which increases inertia and decreases speed. But it also has more mass concentrated around the radius, which increases speed....
  14. J

    Rotational Motion

    Two hoops of identical radii roll without slipping down identical inclined planes under the influence of gravity. Hoop 1 is identical to Hoop 2 except for some massive spokes which are fixed to the rim. If the two hoops are released at the same time from the same height, which hoop makes it...
  15. J

    Simple momentum problems

    Hey, just wanna double check on these: Rain falls vertically into an open boxcar coasting freely on a horizontal frictionless track. As a result the momentum of the system consisting of the boxcar plus accumulated water increases. - I said true - since there is no friction, velocity would...
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