# Search results

1. ### Harmonic Problem

conservation of momentum
2. ### AP Mechanics DiffEQ

Horizontal plane. For anyone interested, I looked up the solutions, and they were able to simplify it greatly with the small angle approximations sin(theta)=theta and cos(theta)=1 Then the torque is -kL2theta, the acceleration is k/[2m]. Then they solved it in one magic step to get...
3. ### AP Mechanics DiffEQ

Homework Statement A stick of length 2L and negligible mass has a point mass m affixed to each end. The stick is arranged so that it pivots in a horizontal plane about a frictionless vertical axis through its center. A spring of force constant k is connected to one of the masses. The system...
4. ### How to find mass with gravitational attraction.

You can calculate the product of the masses with the given force and distance. Then because you know the sum, you have a system of 2 equations with 2 unknowns
5. ### A confusing energy question

The problem deals with conservation of energy. Etop=Ebottom. Without friction, PEtop=KEbottom, but thats not what you have here.
6. ### A confusing energy question

Potential energy only deals with vertical displacement. You need the length of the slide for the second part of the question
7. ### Resultant Force magnitude of the acceleration.

For an angle in standard position (between the x axis and force vector), sine will give the y component and cosine will give the x component. You have to be careful if the question says something like "20 degrees west of north", but here they state each angle is in standard position
8. ### Determine their linear speeds.

Are you using one mass or the combined mass?
9. ### Determine their linear speeds.

The two objects rotate around the center of mass of the system. In this case, the objects have the same mass so the COM is at the geometric center of the system. r doesnt equal the seperation distance, but the distance from the center of mass of the system
10. ### Potential energy

To an extent, we cant really define energy by what it is, only from what we observe it to do. We see something falling off a shelf and say it has kinetic energy. But where did the energy come from? Someone did work against a gravitational field to put it on the shelf, and that was stored as...
11. ### Potential energy

Potential energy is energy of position relative to an arbitrary reference point. It depends on the system of objects and what you define the zero point to be
12. ### Falling Pennies and Force

Because what hurts is when you decide to stop the penny with your hand. Thats the force and acceleration were concerned with
13. ### How to determine X and Y coordinates of launched ball?

The velocity and acceleration must oppose each other as dick said
14. ### Very elementaria kinematics question

The equation v = x/t only works with constant velocity. For non constant velocity but constant acceleration, you can use the equation x=v0t + 1/2at^2. The 4 kinematic equations for constant acceleration can be easily derived using calculus. x=v0t + 1/2at^2 v-v0 = 2ax a = (v-v0)/t v = (x-x0)/t...
15. ### Bohr's theory ?

You could also say that in Bohrs model, electrons exist in discrete energy levels. An elliptical orbit would create energy differences at different points in the orbit. This would lead to constant emmission and absorption of photons spontaneously
16. ### Atwood machine

In reality, the pulley and string have mass, so the experimental acceleration will be less than the theoretical acceleration of the system
17. ### Maximal static friction problem

It sounds like the question should read "minimal static friction constant"
18. ### Help with doppler problem! thanks

8 beats per second means that the difference in frequencies is 8 Hz
19. ### Slightly Confused About Tension

The weight force does do work, W=Fdcos(thete). Because force is opposite of displacement (theta = 180), weight does negative work To check your answers, remember that the new work should be the net force times displacement. The question asks for individual work, so individual forces must be...
20. ### Sound Wave Problem

The only thing that could make this hard is if you wanted to take light into account. It takes some time for light to reach the soldier first, but its almost instant and makes no significant difference
21. ### Delta Symbol confusion

Voltage, like gravitational potential, is in reference to an arbitrary zero point. You can think of the change in voltage in a uniform electric field as the field times the change in distance. But were usually only concerned with the relative change in potential between 2 points
22. ### Photon, Wave/Particle Nature of light questions

All particles have wavelike properties, but usually the mass and momentum are so large that the DeBrogile wavelength is too small to be detectable by any means (smaller than Plank length). The DeBrogile wavelength of certain electrons have been measured and confirmed experimentally
23. ### Light intensity, Max KE of photoelectrons

In order to use 6.6*10-34 for Planks constant, things need to be in Joules. To work in eV for things like energy levels, use 4.1*10-15 eV*s

Looks good
25. ### How are electricity and magnetism related?

When a magnetic field exerts a force on a moving charge, the force is perpendicular to the velocity and the field (right hand rule). In this case, the work done on the particle is zero because force is perpendicular to displacement. Im not sure about the other case where a magnet does work on...
26. ### Missing the point Tangential acceleration

Does tangential acceleration depend on radius? Proportional or inversely proportional?
27. ### How are electricity and magnetism related?

Not usually. The most obvious example of E=hf is an atom absorbing a photon of light, an electron jumping up to a higher energy level, the electron dropping back down to a lower energy level, and emitting a photon. The change in energy is proportional to the frequency of light used, and the only...
28. ### What is the work done by a hiker who is climbing up a hill

Is the elevation a function of x? Neglecting friction, work would just be mgdeltax
29. ### How are electricity and magnetism related?

Youre looking for the equation E=hf. An EM waves energy equals its frequency times Planks constant. This provided evidence for the photon theory and the wave-particle nature of light
30. ### Thin-Film Interference Question. Quick One!

A phase shift occurs when light enters a more optically dense material (greater index of refraction). Youve got 2 boundaries for consideration, the air-gas boundary and the gas-glass boundary. A phase shift occurs at both boundaries, so in order to constructively interfere, the extra distance...