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  1. C

    I think I am making this Work-Energy Problem to Hard

    Homework Statement Figure 7-40 shows a cord attached to a cart that can slide along a frictionless horizontal rail aligned along an x axis. The left end of the cord is pulled over a pulley, of negligible mass and friction and at cord height h = 1.6 m, so the cart slides from x1 = 4.0 m to x2...
  2. C

    Cons. of energy with rotational motion

    your logic is good (except I don't get your second 1/2mv2). You are right about centripital force. At the top the ball needs enough velocity so that its centripital inertia= its weight. The force of gravity must equal its centripital force. This will translate directly into an equation...
  3. C

    Zero velocity and zero acceleraton

    You are fairly close to understanding what is going on. If you throw the projectile straight up, it will have zero velocity at the top but the acceleration will always = 9.8 m/s/s downwards. First it is only stationary (v=0) for a fraction of a fraction of a second. Second it has an...
  4. C

    Tricky Energy Problem

    Homework Statement There is a car of mass 1900kg that travels at a steady speed of 27 m/s up and down a hill. The force of friction is the same in both directions and it takes 49 more horsepower to go up the hill than down the hill. What is the inclination of the hill. Given: mass of...
  5. C

    Speed of an object on a spring

    still way to hard. PE of a spring is equal to 1/2kx^2 where x is distance from equilibrium and KE is 1/2 mv^2. An oscilator is just a system that conserves energy. At one extreme (your initial condition) There is only potential energy of the spring because the object is at rest (it is...
  6. C

    Conservation of Angular Momentum of Ball

    Are you sure? I think that momentum is always conserved even if energy is not. The system is changed by the shortening of the rope and therefore responds with an increase in velocity. If you can make the rope infinitely short, it could go infinitely fast. Dave
  7. C

    Speed of an object on a spring

    I think Dick made things too hard. (no pun intended) Try conservation of energy!
  8. C

    Question about forces

    One more state to be heard from: Ok there are a couple of things going on here and you need to learn how to draw Force Diagrams (they will help you with questions like this) Lets imagine a anvil sitting on a table. 1st:The anvil is heavy (it has a force of weight) 2nd: It is not moving or...
  9. C

    Conservation of Angular Momentum of Ball

    Homework Statement A teatherball is attached to a pole with a 2.0m rope. It is circling at 0.20 rev/s. As the rope wraps around the pole it shortens. How long is the rope when the ball is moving at 5.0 m/s. Note: I can't use the html formating with this site!!! Givens: f(initial)=20...
  10. C

    Non-linear spring

    No, I think your physics is excellent. Sorry 5 years ago I could've helped with the math.
  11. C

    Energy and Momentum

    I am adding on that you may want to consider the Impulse-Momentum Theorum (it should make it easier to deal with force)
  12. C

    Rotational Mechanics - Pulley and Bucket

    I am going to try to put Ja4Coltrane's math into more conceptual terms. Note: Remember those mass/pulley systems. This problem is just a rotational analogy. 1st: You are correct that the only force is the wieght (mg) of the bucket. However F=ma and there are two masses here. Now F is...
  13. C

    Fnet Acceleration Problem

    Listen to cristo but add in one short cut. If you grab a physics book you will find an equation with no time. It looks something like this. vf(squared)=vi(squared)+2ad where v-velocity, a-acceleration and d-distance from there this should be easy. On the last note mechanics is much...
  14. C

    Fnet Acceleration Problem

    Change vi I'm sorry but vi is not equal to 90 mi/hr. The initial velocity is vi=0 (the key word is at rest). vf=90 mi/hr but this is useless until you convert to m/s. Now you know vi, vf, xf, xi=0, so plug into your equation, do some algebra to isolate acceleration and this is easily...
  15. C

    Specific Heat and Phase Change/Latent Heat Problems PLEASE HELP

    You need to listen to lightgrav, You must do the problem in 3 steps (+1 for the Al.) Take the enrgy lost. (You do this correctly) but do it three times just as lightgrav says but you can use Celcius instead of Kelvin. Use Q=mL only for the phase change Water to Ice. Then you must do 1...
  16. C

    Flying ring

    You have a good start You have the avg. velocity part right and you need to solve for time. Hints. 1. What is the avg. acceleration (this is the key to the problem) 2. You can use the 4 eqns. of motion to solve any other question you asked. 3. Be very careful with negative signs...
  17. C

    Maximum height?

    Question 1 only Hints: 1. Listen to Skippy. 2. The motion is symetrical. So it takes half the time to go up and half the time to come down. 3. Somewhere (book, online) you can find the velocity of any object at the top of its tragectory in freefall motion. It is always true. 4...
  18. C

    Speeding cars

    Ok you have two equations of motion 1 for constant velocity and one for constant acceleration. Now you have two options. Solve both equations for displacement/distance and make two data sets. I suggest graphing both data sets on a shared set of axes. Make time the hotizontal axis and...
  19. C

    Effect on electron in magnetic field

    try this I see two forces here (sort of, one is a consequense of the other): 1st force (the real one): The electromagnetic force Look at what you have: B-field, velocity, charge (its an electron) 2nd force (implied in the motion): Centripital Force What the first...
  20. C

    Questions on kinematics (distance/velocity/acceleration)

    Solving the slope I don't think that you need to take the derivative especially if you are not in a calculus based physics course. To find the slope at one point draw a tangent line. I promise there is an explantion of how to do this in your book. It should just touch the curve. The...
  21. C

    Simple harmonic movement problem

    Listen to mukundpa he put you on the right track but I want to add a couple of things. 1) Make sure your units match. If you use gravity in m/s^2 your distances must be in meters. (otherwise you can convert gravity to cm/s^2) same thing. 2) You need an eqn. for acceleration b) if...
  22. C

    Initial speed physics problem

    solving part b Part b) is actually quite easy but you must remeber to add 24 meters (thx Mozart) to your final answer. Lets look at what we are given: v initial = 9 m/s acc = -9.80 m/s^2 (gravity) Now lets look at the things we must assume: lets set initial height to zero so that we...