# Recent content by davidchen9568

2. ### Quantum Harmonic Oscillator

You are missing an x^2 in #3.
3. ### Variable mass system - sand falling on flatcar

F=ma can be applied, but that will only make the problem more complex. If you apply it to (flatcar + sand on it), you need to find the forces acting on the system. Sand falling on the flatcar exerts a force to it, because friction has to act on the sand to accelerate it until its velocity equals...
4. ### Efficiency of a engine

Thanks for the reply. Now the problem is solved. Diesel cycle - Wikipedia, the free encyclopedia
5. ### Efficiency of a engine

Homework Statement Four thermodynamic processes A,B,C,D are shown in the picture. A and C are adiabatic processes. Pressure is held constant during B, and volume is constant during D. An engine run from A->B->C->D->... What is the efficiency of this engine (in terms of V1/V2)? Homework...
6. ### Integrating dx/dt=k(a-x)(b-x)

In the original post. t=0 when x=0.
7. ### Magnetic Induction (Non-uniform Current)

Because J is a function of radius. I=\int { J\cdot dA } The second method looks fine. For the second question: What is the enclosed current outside? Is it zero?
8. ### Integrating dx/dt=k(a-x)(b-x)

Looks like I get x=\frac { a{ e }^{ r }-b }{ { e }^{ r }-1 } \\ r=(b-a)(kt+c)
9. ### Integrating dx/dt=k(a-x)(b-x)

What are the values of a,b, and k?

11. ### Question about Eötvös experiment

I do not understand the concept. Let the centrifugal forces on the two objects are F1 and F2. The rod will not rotate because net torque is 0. That is, F1r1=F2r2. That Does that mean we have to carefully adjust the positions of objects (before experiment) so that m1gr1=m2gr2? Then we conclude...
12. ### Help with piston and atmospheric pressure

P1 is the initial pressure. Look at the piston. There is a upward force produced by air inside, which equals P1 times S. Two downward forces are atmospheric pressure and weight. This gives the first equation, and the second one is similar.
13. ### Finding max. velocity of jet w/ constant and/or changing acceleration

In the case when mass changes (because of fuel), F=ma no longer helps. Try F=dP/dt

Looks good.
15. ### Triangle Inequality Proof

Write down the triangle inequality. You need a minus sign, which can be obtained by moving something to the other side of the inequality.