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510
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location San Mateo, CA
age 59
visits member for 2 years, 11 months
seen 3 hours ago

Apr
10
comment Kepler's third law doesn't give earth's orbital period! Why?
An error of one part in $10^4$ is quite reasonable when one of the inputs has only three digits of accuracy. That is much larger than the planetary perturbations.
Apr
2
comment What is the maximum range of a bullet flying through the sky?
The fact that the bullet transitions from supersonic to subsonic makes the air resistance very hard to calculate. It becomes a better candidate for experimentation.
Apr
2
comment What is the maximum range of a bullet flying through the sky?
The reason the websites work in vacuum is because it is easy. Two constants ($g$ and initial velocity) and you are done. Air resistance is hard. You need to specify the bullet carefully, but the drag coefficient varies with velocity.
Mar
27
comment How to calculate the velocity needed for a rocket to get to a L1 point (escape a body without orbiting)?
Your question misses the point that the L1 point is rotating around the earth at the same angular velocity as the moon. Your image is to get to L1 with zero velocity in inertial space, which is a well-defined operation and DavePhD has shown how to calculate the energy requirement for that. However, it is incorrect to think you will just "fall to the moon" from there. The moon is running away from you with its orbital velocity. You have a lot of sideways velocity relative to the moon, so are likely to miss.
Mar
25
comment How do we know that earth is not perfect sphere?
I didn't flag this as not an answer, but precession only shows that the moments around the principal axes are not equal. The earth could be spherical with a nonuniform mass distribution and produce this data.
Mar
14
comment what determines the wavelength of waves on the open ocean?
Generally these started life as wind waves. The height increases with wind velocity, duration, and fetch. Once generated they travel long distances with little attenuation.
Mar
13
comment What are the means to consider that a specific function is phase of an oscillator?
Yes, the amplitude of 1 is the range of the inner cosine function. If you want it to be truly periodic, you need the modulation to have a period that is (a multiple of) the period of the main wave. But if you think of phase modulating a data transmission the function would be $\cos (\omega t + data)$ where data is not periodic. The resulting wave is not truly periodic, but it is close enough for many purposes to be considered periodic.
Mar
12
comment Work-Energy-Power Relations
I think you are missing that more air passes the turbine as the velocity increases.
Mar
6
comment Do photons interact only with single partles or can a single photon be absorbed by 2 or more particles simultaneously?
When you say no interaction, each particle is excited by the field at whatever time it wants. They might not be at the same time.
Mar
6
comment How would you go about finding the natural frequencies (resonance frequency)
There is no natural frequency for materials. There are natural frequencies for objects, which have vibrational modes with frequencies. Please think about what you are trying to ask.
Mar
5
comment Feynman diagram for pair production in matter
A particle in a Feynmann diagram that does not go off to infinity need not satisfy $E^2=m^2+p^2$ As it lives a short time, it is covered by the uncertainty principle.
Mar
5
comment Feynman diagram for pair production in matter
It satisfies energy and momentum conservation, but the electron that leaves and interacts with the nucleus need not (and will not) be on the mass shell. That gets rectified by the interaction with the nucleus.
Mar
4
comment Why does a remote car key work when held to your head/body?
Are you accusing OP of having a hole in his head?
Mar
2
comment Solar panel maximum efficiency at specific frequency and temperature?
If the intensity gets small enough, there are probably losses that stop the cell from producing power, but I don't know.
Feb
27
comment What is the acceleration of a two weights connected with wire?
Beacuse it is accelerating at $\frac 13g$
Feb
27
comment What is the acceleration of a two weights connected with wire?
The force in the wire has to support $m2$ against gravity and pull enough to accelerate it by this amount, so$ F=m2(\frac 43g)$
Feb
27
comment How much time would take to lift a person to 0.1m above floor of elevator?
Looks good to me
Feb
26
comment What is the cause of centripetal/centrifugal force?
The force away from the center, which comes from the non-inertial coordinate system, is centrifugal force. The force toward the center, which keeps the object in orbit, is centripetal force. It can come from various sources: gravity, EM, tension in a string, etc.
Feb
26
comment How to calculate how many can a stick hold?
Are you trying to calculate the weight before the stick breaks? Is the weight concentrated at the center, evenly spread, or what?
Feb
24
comment Does the ground beneath a levitating object change due to the rotation of the earth?
To calculate what happens,you need to define the forces acting. I am claiming that "hover" does not do that-there are a number of interpretations that lead to different lateral forces. Each leads to a different answer. The first two choices have no equations and seem to me accessible. If I ask a helicopter pilot to hover above a point, he will maintain the craft above that point. Any disturbance, like wind, he will do something about. That says there will be no drift. If I tell a copter to maintain altitude, it will do nothing about lateral motion.