# Search results

1. ### Dynamics help: variable acceleration and angular velocity

For question 1, start with the Kinematic Equations, specifically v = u + at
2. ### Big Bang: A silly question

The Earth and Moon are gravitationally bound to each other, but due to external forces the Moon is gradually moving away from the Earth at a rate of 3.8 centimeters per year. This is not due to the expansion of the Universe. In fact, galaxies as a whole are gravitationally bound i.e. a galaxy...
3. ### MATLAB Matlab ode45/independent variables help

Hi - I'm having some difficulties with a simulation I'm writing. I have a second order ODE with three arguments of derivative information y(1),y(2),y(3) - each changing wrt to the independent variable t. Currently, in my system of ODEs, I have a variable that I am treating as constant...
4. ### MATLAB Matlab 2nd order ODEs for Rocket Ascension

I've written a program to show the trajectory of a rocket around the Earth with initial conditions that can be manipulated to fix a circular or elliptical orbit. We start with Newton's 2nd law and use the equation a=F/m in freespace (so m can divide out) to get a 2nd order ODE and solve by...
5. ### Finding Average Speed

lol my mistake. obv meant 10km/hr
6. ### Finding Average Speed

Yes, and he still spent an extra 19.2 mins on the trip. You can't just forget about that time. Just think about running around your block. If you run at a constant speed of 10km/hr, your average speed is obviously, 20km/hr. But if you stop for 30 seconds to take a breath halfway through...

8. ### Finding Average Speed

Don't forget the time spent getting gas (speed = 0). You'll have to include that

Use the relation between heat capacity, mass, temperature and heat. Look up values for heat capacity, specific heat capacity and latent heat of fusion/melting for water.
10. ### How do you find wavelength if your given only the speed?

You would need to know something else - either the frequency and the medium through which the wave moved, or the distance the wave travelled and the number of modes.
11. ### Satellite orbital speed homework

Use the fact that to remain in a circular orbit, the gravitational force must equal the centripetal force. You do not need to know acceleration of the satelite
12. ### Two-block system - what am I doing wrong?

Yes, you should have Frictional force acting in the x direction = u_k * N_B However, your leading term: N_B which stands by itself should not be there. N_B is the force that the ramp exerts on the block, and while it is an important term in determining the frictional force, it in itself...
13. ### Two-block system - what am I doing wrong?

your meaning of x component of weight of block B seems to be the same as my meaning of x component of gravity. Gravity is dragging the block down the ramp, but not at the rate mg, it is damped by a factor of sin(theta) of which you have written down correctly. N should not be there
14. ### Two-block system - what am I doing wrong?

No your Tension looks like the right sign, but if your W is the 'x component of gravity' term then that needs to be positive, since it's directing your block to the right. There is no x component of a Normal force so leave out N. Keep note that your coordinate system doesn't matter, but...
15. ### Two-block system - what am I doing wrong?

As far as I can tell your math is good, but I don't think you need this 'weight' term in Fnetx B. Your terms in Fnetx B should be Tension - Friction - xcomponent of Gravity
16. ### Two-block system - what am I doing wrong?

What does it represent? It's not Tension, it's not Friction....
17. ### Two-block system - what am I doing wrong?

What is the W term in your Fx B eqn?
18. ### Two-block system - what am I doing wrong?

Are you looking for someone to tell you you're correct, or is your solution wrong?
19. ### Energy Equations

Start with Newton's Laws, write down the equations of motions and go from there
20. ### Orbital Speed of a Star -

Orbital Speed of a Star - Please Help! Homework Statement Calculate \Omega(r) and v(r) for the following density models: (a) all the mass M is at the center of the galaxy; (b) a constant density adding up to a mass M(R0) at the Sun’s orbit and no mass beyond. Homework Equations...
21. ### Quasar Help

I see, so are we assuming that it can only extend to a maximum size of 4 light months? 4 light months corresponds to roughly 3.1 e15 meters, which is about 1000 times the size of the S radius of the black hole. Does this sound right?
22. ### Quasar Help

Homework Statement If a quasar varies on a time scale of four months, how does the maximum size of the emitting region compare with the Schwarzschild radius for a 109 MSun black hole? Homework Equations The Attempt at a Solution Calculating the S radius of the black hole is...

Homework Statement Calculate \Omega(r) and v(r) for the following density models: (a) all the mass M is at the center of the galaxy; (b) a constant density adding up to a mass M(R0) at the Sun’s orbit and no mass beyond. Homework Equations M(r) = v(r)2r/G The Attempt at a...

25. ### Central Pressure of a Star, help please.

solved. thanks a lot
26. ### Central Pressure of a Star, help please.

ok ill try ty
27. ### Central Pressure of a Star, help please.

Ok well I plug in the values to get the following: -G4\pi\rho02 * 1/r2 * (r3/3 - r5/3R2)(1 - r2/R2) which simplifies to -G4\pi\rho02(r/3 - 8r3/15R2 + r5/5R4) How can this possibly be right? since there are \rho0 terms in there? Ugh
28. ### Central Pressure of a Star, help please.

right ok my bad, but now if I plug that into HE equation -GM(r)\rho(r)/r2, I get a huge mess that probably won't turn into my answer. What am I missing?
29. ### Central Pressure of a Star, help please.

Oh right the different limit gives a different answer than M(R) so it would be 4\pi\rho0[r3/3 + r5/5R2] Am I right?
30. ### Central Pressure of a Star, help please.

you said the same as M(R) so I integrated 4\pir2\rho(r) with limits 0 to r