Recent content by Kelju Ivan

  1. K

    VAWT, wind induction factor

    I'm trying to model a vertical axis wind turbine with the double-multiple streamtube model (with Matlab), where wind speed is dampened by an induction factor so that the output is different for upwind and downwind parts of rotation. The trouble is that for the downwind part, the induction...
  2. K

    Convective heat transfer coefficients

    Hi. I'm trying to make a simple model of a condensation based countercurrent heat exchanger where liquid water and steam flows are separated by a conducting wall. I formed the equations as Q = \frac{T_{steam}-T_{water}}{\frac{1}{Ah_{water}}\frac{d}{Ak_{wall}}\frac{1}{Ah_{steam}}} = L\dot{m}...
  3. K

    How does electricity power devices?

    Hmm. Alright, thanks for the answers everybody.
  4. K

    How does electricity power devices?

    Thanks for the answer, but that really wasn't my question. I was trying to find a general answer, why does any electric device work. What good are mobile electrons in devices which aren't meant for generating radiation, like computers or food mixers? Somehow the electrons manage to make things...
  5. K

    How does electricity power devices?

    I've been wondering how or why electricity actually works. Resistance heaters and light bulbs just turn the kinetic energy of electrons into heat, but what about more complex devices? For example, why does a microwave oven do something useful when electrons flow in the circuitry?
  6. K

    2 Question involving momentum and collisions

    1) You can solve easily solve the momentum of the snowball. Then you need to solve its y component with the help of sine. Because momentum is conserved, the net y-component for the whole system must be zero, so the sled gets an equal but opposite increase in momentum (towards south). Of course...
  7. K

    Potential Energy Car Downhill Question

    What exactly did you do here? It looks like you took square roots of some of the numbers separately, which really isn't allowed. The first equation is correct and you can solve for V simply by diving both sides with 550kg and then taking the square root. You should note however, that all the...
  8. K

    How far the peg is driven into the ground due to impact?

    Wouldn't it be simple to use kinetic energy. The peck has some kinetic energy and the ground does negative work to the peck with a force of 1kN. Just find when the kinetic energy equals the work done by the ground.
  9. K

    Schools University & Physics

    I believe undergradute means Bachelor's degree and graduate stands for Master's degree. Don't know for certain, since I'm not from USA either. In here between a master's and a doctorate there's licensiate (or some such).
  10. K

    Cooling trouble

    That differs a bit from the answer we were shown, but I guess it does just the same thing, you just used Boltzman's constant instead of R. In our version we had C_p=\frac{7}{2}R . I'm not really sure when I should use 5/2 and when 7/2, since both are valid for C_p. t=Q/P where...
  11. K

    Cooling trouble

    Air conditioner cools the air in a room with a power of 8.4*10^6J/h. Volume of the room is 62.5m^3. At first the air is at the temperature of 30C and air pressure is 1atm, which stays a constant. How long does it take to cool the room to 25C? Note that the air shrinks while cooling down and...
  12. K

    Ideal gas problems

    There are some problems which have me completely stumped. 1. A balloon has a volume of 10.5dm^3. Its mass is 8.5g and inside is helium at a pressure of 1.05atm. Atmospheric pressure is 1.00atm and both the helium and the outside air is 25.0C (degrees Celcius). Define the tension in the...
  13. K

    Hello everyone, Angles

    Maybe it's not too late to do some creative censorship. .)
  14. K

    Addition of Forces

    But once you find the mass, you can calculate the weight. The net force in the x-direction causes the acceleration given. You know the relation between force, mass and acceleration, so you can solve the mass.
  15. K

    Who's using here?

    I would use Mastering Physics, but my professor hasn't activated the thingy and put up any exercises. I tried it last year though. Seemed quite useful, though typing all the more special characters was a bit of a chore. Don't have a clear memory anymore...