# Search results

1. ### Vertical Kinematic Problem

Homework Statement A stone is dropped of a cliff. A second stone is thrown down the cliff at 10 m/s at 0.5s after the first stone. When do the stones cross paths? Homework Equations Yf = vt + at^2/2 The Attempt at a Solution My logic is the set the final position Yf equal for both stones...
2. ### Throwing a rock up a hill

Yep, got it. I was on the wrong track. . . I would shoot myself in the foot, but instead I may get rid of it altogether! Thanks for the help and quick replies.
3. ### Throwing a rock up a hill

Getting rid of time; the only way I see that is if I substitute t = \frac{x_f}{v_x} , giving us y_f = x_f tan(\theta) + \frac{1}{2 v_x^2} a_y x_f^2. Perhaps I do not understand, we do not know y_f , nor x_f .
4. ### Throwing a rock up a hill

I tried this but here is what I got: y_f = x_f tan(\phi - \theta) + \frac{1}{2}a_y t^2. Still too many unknowns though, assuming my algebra and logic is correct of course.
5. ### Throwing a rock up a hill

Homework Statement I was tutoring the other day, when we came across a problem that had me stumped! A person standing on a hill that forms an angle \theta = 30^o wrt to the horizon, throws a stone at {\bf v} = 16 m/s up the hill at an angle \phi = 65^o wrt to the horizon. Find y_f...
6. ### Lagrangian for a free particle expansion problem

Hello, this is probably one of those shoot yourself in the foot type questions. I am going through Landau & Lifshits CM for fun. On page 7 I do not understand this step: L' = L(v'^2) = L(v^2 + 2 \vec{v} \cdot \vec{\epsilon} + \epsilon^2) where v' = v + \epsilon . He then expands the...
7. ### Horizontal Pulley Question [Forces]

Perhaps, think about a force diagram. You have one force going downward and one upward. Draw it out, then solve for your unknown.
8. ### Question about eigenvector and identity matrix

Every vector is an Eigenvector of the identity matrix. Perhaps I do not understand what your saying. . .
9. ### Proving properties of the Levi-Civita tensor

You are absolutely correct! The definition of the Levi-Civita (i.e. swapping (non-cyclical) => minus sign).
10. ### Centrifugal Force, Centripetal Force, and Space

The centrifugal force is not an inertial reference frame, as you said fictitious.
11. ### Horizontal Pulley Question [Forces]

What do you think the acceleration of the falling object is?
12. ### How many ways to put 100 distinguishable particles into 6 boxes?

Not to sound redundant, but the key word here is: combinations
13. ### Elementary Wave Functions

Do you need to use Mathematica? Just use integral table or or solve it as mentioned above. In all my QM courses, we never used Maple, or Mathematica.
14. ### Problem with integrals

Okay, also note that \int \cdots \int f(\vec{x}) \delta(\vec{x} - \vec{x}_o) d^Nx = f(\vec{x}_o). This can allow you to fix some variables. My next question is, are we integrating from -\infty \rightarrow \infty ? If the variable being integrated is not within the bounds, we can simplify...
15. ### Problem with integrals

What have you attempted? Do you understand the properties of the delta function?
16. ### Relationship between Frequency and Standing Waveforms.

For increasing frequency, the number of nodes will increase as well. Draw several diagrams, double the frequency each time. Then you can deduce how frequency affects the nodes and antinodes.
17. ### Showing the expectation values of a system are real quantities

Hmm, perhaps forget what I mentioned previously. You simply need to reconsider your wave function. Perhaps try something of the form \psi = e^{\pm i(kx-E t/ \hbar)} . . .
18. ### Pebble dropped on rotating wheel, starts to slide after rotation

Try drawing a force diagram. This always helps. I am sure you can think of some relevant equations.
19. ### Weight at an Angle

90 - 40 = 50. Not 55.
20. ### Showing the expectation values of a system are real quantities

You wave function is incorrect. Do not plug it in until you have done the math. You do not even need a "test" wavefunction for part a.
21. ### Urgent: Angle of Projectile

You don't. tan(\theta) = \frac{d_x}{d_y} Solve for \theta
22. ### Urgent: Angle of Projectile

If you know x and y (or v_x and v_y), you can find the angle. Who is the man? Tan is the Man! Recall SOH CAH TOA
23. ### Electrodynamics Potential from charged sphere. I am lost :/

If I had a nickle every time someone says "I plugged it into maple". . . Also, a table of integrals comes in very handy for EM problems.
24. ### Frequency of a simple harmonic oscillator

Also note that \omega = 2 \cdot \pi \cdot f . You now have all the tools, just solve!
25. ### Quantum Um vs Classical Um

I am assuming that for high T you can manipulate e^{\frac{h \nu}{k T}}. Try this.
26. ### Quantum Um vs Classical Um

Pardon my ignorance (I have never heard of this in all my years in physics), but what is Um?
27. ### Gauss Law

Perhaps, we can treat this similar to the case for an infinite wire? Are we finding the E-field at some point say on the y-axis, or some point on the x-axis? Must we use Gauss's Law?
28. ### Gauss Law

Yes, really what we have is a point charge in one dimension, where we only consider the charge density along the x-axis. I suppose a cylinder would be fitting for Gauss's Law. Yes, you are correct about integrating along the x-axis.
29. ### Total charge from charge density (spherical coordinates)

dV = r^2 \sin(\theta) dr d\theta d\phi
30. ### Gauss Law

Is x a vector? If not, assume one dimension. Your surface area will most likely be of a sphere. Also, recall that q_{enc} is the total charge. Can you think of another (more formal) way to write q_{enc} ?