On the picture, ##ABCD## is a parallelogram, ##(EF) // (AB) ##, and ##(GH) // (BC)##.

The problem is : show that lines ##(EB)##, ##(HD)##, and ##(IC)## either all meet in ##M##, or are parallel.

geometry question -- several lines through parallelograms]]>

Zeroth component of 4-momentum & energy-momentum relation]]>

200lb Capacity Book Bag]]>

Differentiating twice under the integral (with assumptions)]]>

How are Mixed State Ammonia Molecules Separated by an E Fld?]]>

A 1350kg car travelling at 72km/h collides with a slow-moving car of mass 1650kg, also initially travelling south. After the collision, the velocity of the 2 cars together is 24km/h. Determine the initial velocity at which...

Initial Velocity of a Car]]>

Acceleration a

F = ma

The equations I've gotten so far:-

1) N1sin(theta) = m2a

2) m1gsin(theta) = m1a1

3) m1gcos(theta) - N1 = m1a2...

(somewhat complex inclined plane problem) why is this wrong?]]>

An advanced example in fortran 77]]>

A changing focus from Art to Engineering]]>

Estimate the rate of continuous creation required to keep the density of the universe constant at 10

Assuming a spherical matter-dominated Friedmann universe, we know from solving...

Rate of continuous creation]]>

https://drive.google.com/file/d/0BxPEJS0qVOpeWENSREI1RlNsNDQ/view?usp=sharing

A hub is connected to a shaft with a shrink fit (pressurized oil assembly, grease removed). The material of the hub is quenched and...

Safety factor, temperature and torque]]>

I'm trying to calculate the Fourier Series for a periodic signal defined as:

y = x 0<x<2Π

y = 0 2Π≤x<3Π

Fn = 1/T ∫T f(t)cos(kwοt + θk)

cn/2 + ∑k=1k=∞(cn)cos(kwοt+θk)

cn= 2|Fn|

θk=∠Fn

Fourier Series neither even nor odd]]>

A: (1,3) (1,0

B: (0,0) (2,1)

C: (3,1) (0,3)

How would one go about finding an optimal mixed strategy for something like this? I mean, if this was a 3x3 matrix then one...

Game Theory: Strategy for game with non-square payoff matrix]]>

This time the format is a bit different. We present 10 statements that are all of the nature ##P## if and only if ##Q##. As it turns out, only one of...

Aren't you tired of counterexamples already?]]>

Numerical vs. Monte-Carlo Simulations]]>

We know that this is observationally false, since in fact ##\ddot{a}>0##.

But why do they assume this?

My guess is that in the big-bang model...

Inflation assumes ##\ddot{a}<0## after inflation?]]>

Code (Matlab M):

Just a general physics question that I was thinking about. I posted it here because I assumed it is a general question that is easy to most experts. I apologize if something similar was posted before, but I couldn't find...

Which mass to use in a momentum change problem?]]>

you do this simple math and you get an number that is in KE units , Joules.

so, why is the KE unit equation, 1 Joule = Kg x (m^2/s^2) ??

1Kg traveling at 1m/s would have a KE of 1Joule, but using the KE equation, it would be 1/2 a Joule.

why is...

Physics 101 refresher question -- Confused about the definition of a Joule]]>

Is it possible to find this? Really only need the semi major axis or even it's orientation.

In the image below, elements in red are known....

Ellipse from 2 arbitrary points, tangent at P1 and focus]]>

I wonder what makes thunder sound the way it does. I don't really understand lightning either but it is more easy to understand why it sounds. But what makes thunder sound? What happens up there in the sky?

Best regards, Edison

PS

I see now that there is a similar thread already, in spite...

What is thunder?]]>

Assume that there is a deviation from Coulomb’s law at very small distances, the Coulomb potential energy between an electron and proton is given by

[itex]V_{mod}(r)=\begin{cases}...

Perturbation first order hydrogen - Coulomb model]]>

I am curious on designs for a system that will take the energy from a...

Charging EV with varying input power]]>

What exactly is Plasma?]]>

Diverting my students' interest]]>

I have a flash drive that I have already put a few files on that cannot be deleted by any user other than me on my own computer, but I recently found out that anyone can reformat the flash drive and get past that. Is there any way that I can be able to read and write to and from the...

How can I protect my flash drive from reformat?]]>

In...

Can a Photon be Absorbed Without the Exact Energy Level?]]>

V=IR

3. The attempt at a solution

The Vt(v total) is 30v

so,must i ignore the diode as off...

Diode two dc sources]]>

I have two novice question

If the universe is expanding and it is all moving apart, how is it that galaxies are colliding?

If our galaxy and all others are moving away from some singularity central point. And as we see other galaxies moving away from us at a speed relative to there...

Can we identify the centre of the Universe?]]>

Suppose we have a folding ladder, so that when its legs are spread it makes an isosceles triangle. Suppose it has a support that runs parallel to the ground. There is a bucket of paint that rests on top of the ladder, and the...

A simple static equilibrium problem]]>

Hi everybody! I'm really struggling with those exercises from my special relativity class, and I'd like to know what you think about that one because I come up with a strange result:

The motion of a point mass in a plane is...

Elliptic path, normal and tangential acceleration]]>

Here is the last page of part 4. https://www.physicsforums.com/threads/random-thoughts-part-4.786642/page-201]]>

International Physics Studies Program (IPSP) University of Leipzig program review?]]>

I once read that Carl Sagan proposed the idea by spreading bacterias in...

Venus, terraforming]]>

Misconceptions about Virtual Particles

...

Misconceptions about Virtual Particles - Comments]]>

This is what I know

- u(t) = sqrt(2)*220*sin(314*t+π/3)
- R = 10 Ω
- L = 3 mH
- C= 3 mF

Graphing the energy in an capacitor, coil and resistor]]>

Am i good for physics?]]>