Recent content by rtsswmdktbmhw

A number of my relatives believe that radiation from cell phones is dangerous. After doing a bit of reading, I've found that the general scientific consensus is that this is not the case, and I myself don't see how low power, low frequency, non-ionising radiation can cause e.g. brain tumours -...

You don't need to calculate initial velocity - it is 30 m/s at 60 degrees. But to solve your problems, you will need to calculate the vertical and horizontal components of the initial velocity.

How would you explain the mechanism for heating up via radiation (in a vacuum)?

The net force you exert in lifting the block is equal to mg=100N up, and net force times distance h is mgh. As previously said, the block doesn't lift itself so it doesn't make sense to take the net force on the block. The work done by the block is ziltch, the work done by you in the lifting the...

Temperature is dependent on the kinetic energy of the particles in the object. So if the object loses energy, temperature decreases accordingly.

You are using Galilean transformation to add the 40 mph instead of Lorentzian transformation. Here are the wiki pages for both: http://en.wikipedia.org/wiki/Galilean_transformation http://en.wikipedia.org/wiki/Lorentz_transformation Basically (from wikipedia): ". . . Galilean transformation can...

The block doesn't lift itself. In other words, it's not doing the work to increase its own potential energy.

Large mass gives higher gravity, it doesn't necessarily have to be in a small area.

Oh, whoops, I meant comparing, not equating, the 0.5*m*v^2 (before collision) with 0.5*I*omega^2 (after collision), where I is the rotational inertia of wheel+dart and omega can be worked out via conservation of angular momentum.

Ok, thank you very much for the help!

What friction is this? Is it due to the fact that the dart stuck to the rim? Wikipedia says that inelastic collision is one where the two objects e.g. carts stick after collision, but I wasn't sure if that would apply here since that dart has a sharp end. Yes, this is usually what I would do as...

Hm, well the magnitude doesn't change but wouldn't the direction with respect to the second origin be different? But, I gave it a shot (below). Okay, so let ##\vec r_2=\vec r+\vec a## and ##\vec v_2=\vec v## then ##\vec l_2=(\vec r+\vec a)\times m\vec v## and so ##\vec l_2-\vec l=(\vec r+\vec...

Homework Statement Bicycle wheel is at rest, and can rotate frictionlessly about a fixed axle. A dart travels at velocity v (in plane of wheel) parallel to a line that goes through the centre of the wheel. It hits the rim of the wheel and sticks. What kinetic energy, if any, is lost during...

Homework Statement At time t, particle with mass m has displacement ##\vec r (t)## relative to origin O. Write a formula for its angular momentum about O and discuss whether this depends on choice of origin. The second part is what I'm more unsure of. Homework EquationsThe Attempt at a...

Okay, thanks for your explanations! And also for the tip for ##\hbar##.