# Search results

1. ### St. Louis Motor simple question

It alligns with the magnets but then does not spin. It seems like it would just spin fliping the polarity of the electrical current but it behaves exactly the same.
2. ### St. Louis Motor simple question

I am building a St. Louis Motor for a project in my AP physics class. I followed the directions the best i could and my physics teacher said it looked good but it does not seem to work. I tested it for continuity and it looks good. My math teacher thought that maybe the neodymium magnets i am...
3. ### 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...
4. ### 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...
5. ### 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...
6. ### 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...
7. ### Scale? -- mass or weight

Listen to Doc Al and Jakell. When your scale reads 70 kg what it is really doing is weighing 686N and just dividing by 9.8m/s2 and giving you a reading in kg. It assumes your mass from your weight becuase the kg it is a usefull unit. In your post you mentiong 70 kg. Now on earth that will...
8. ### Eyes FPS

I don't know a ton but I do know that what is usually measure is not fps but rather the speed at which you start to see movement as non-continous. This is about 60 Hz. Anything giving off light faster than that will apear to be continous. Therefore anything changing withing that region will...
9. ### Color Theory Modeling?

I understand the basics of color theory and I need to explain it to some graduate level bio-students. Now I need to incorporate the biological funciotions involved in this process and relate it to avian species. Now I have a brief understand of the human eye abosorbtion curves which peak at...
10. ### 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...
11. ### 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
12. ### Speed of an object on a spring

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

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...
14. ### 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...
15. ### Non-linear spring

No, I think your physics is excellent. Sorry 5 years ago I could've helped with the math.
16. ### 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)
17. ### 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...
18. ### 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...
19. ### 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...

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...
21. ### Good Beginner Book

Thanks :smile: Thanks for all the suggestions. I will definitly look into most. I will probably start with the basic physics test and I have a few halliday resnick (don't we all).:biggrin:
22. ### 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...
23. ### 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...
24. ### 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...
25. ### Disagreements between physics and math departments.

Buy a Guide As far as the original question they math people tend to be more intersted in proofs and the physics people in aplication. (this is a generalization but it often holds true). If you stick with physics though you will find that the people who double major in math and physics tend...
26. ### 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...
27. ### 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...
28. ### Good Beginner Book

I have a student that is interested in learning some quantum physics at the conceptual level. What you be good reading material to start with. We can do a little math but I am in a high school setting. Any suggestions appreciated. curly
29. ### 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...
30. ### 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...