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  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

    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...
  5. 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
  6. J


    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...
  7. 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...
  8. 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...
  9. J

    Elastic collision

    A cart of mass M and a second cart of mass 2M collide head on elastically and bounce apart. Which cart experiences a larger magnitude of acceleration during the collision?
  10. J

    Magnitude of Total Momentum

    Say there was 2 collisions. There are 2 carts of identical mass. In the first case cart A starts at height h above the ground and crashes into cart B which is stationary on the flat ground. They stick together. In the second case, cart A starts at height h/2 above the ground, cart B starts at...
  11. J

    HELP! Block up incline

    There's a block of mass M that's pulled up an incline by a force T. The block starts from rest and is pulled a distance L by the force T. The incline, which is frictionless, makes an angle (a) with respect to the horizontal. 1) Write down the work done by force T. That would just be W =...
  12. J

    HELP! mechanics problems

    Hey, can any of you clarify a few things for me? I'd greatly appreciate it, thanks! If the work done on an object is by conservative forces, does that mean the momentum is conserved? I know if there aren't any external forces, then momentum is conserved. Does conservative forces mean no...
  13. J

    Really simple problem - can't get right answer!

    Suppose a 50kg block slides along a horizontal surface where the coefficient of kinetic friction between the block and the surface is uk = 0.60. A force F = 400 N is now applied, where the angle of the force above horizontal is 20°. What is the magnitude of the acceleration of the...
  14. J

    Circular Motion - please help

    Circular Motion - please help ASAP!!! Two identical blocks are tied together with a string and placed along the same radius of a turntable that is spinning about its center. The inner block is 4 cm from the center and the outer block is 6 cm from the center. The coefficient of static friction...
  15. J

    Lines and Planes in Space - HELP SOON!

    I am very confused regarding a few problems in Calculus III. Any help or hints to any of these would be greatly appreciated!! 1.) Are lines L1 and L2 parallel? L1: (x-7)/6 = (y+5)/4 = -(z-9)/8; L2: -(x-11)/9 = -(y-7)/6 = (z-13)/12; The answer says that they are parallel, which I...
  16. J

    Physics 1D problems: Please help !

    Problem 1 Ball A is dropped from the top of a building of height H at the same instant ball B is thrown vertically upward from the ground. First consider the situation where the balls are moving in opposite directions when the collide. If the speed of ball A is m times the speed of ball B...
  17. J

    Find the distance d that places the final image at infinity.

    Anyone know how to solve the following problems? Thanks! 1.) An object is placed 12 cm to the left of a diverging lens of focal length -6cm. A converging lens of focal length 12 cm is placed a distance of d to the right of the diverging lens. Find the distance d that places the final image...
  18. J

    E & M Question: Please help !

    Hi, I was wondering if you can help me with the following question. I am totally stuck. I'm not sure I even understand the question. Any help or hint would be greatly appreciated! This is the problem: Over a region where the vertical component of the earth's magnetic field is held in an...