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  • Users: xelda
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  1. X

    De Broglie wavelength of an electron and speed

    Awesome. Thank you so much for your help!
  2. X

    De Broglie wavelength of an electron and speed

    Homework Statement An electron has a de Broglie wavelength of λ = 6.4e-10m. What is its speed? What voltage was needed to accelerate to this speed? Homework Equations v=h/mλ KE = 1/2mv^2 The Attempt at a Solution I already determined that the speed is 1.136e6 m/s. Finding the...
  3. X

    Help me figure out these true/false statements.

    Thanks for your help! I can understand your explanations, but could you elaborate more on number 6? From what I've interpreted in the textbook, the total energy would be conserved due to the law of conservation of energy, isn't it?
  4. X

    Help me figure out these true/false statements.

    1) A ball is thrown from a tall building at some angle with respect to the horizontal. By measuring the height of the building and the distance that the ball lands from the base of the buiding, one can uniquely determine the speed of the ball when it hits the ground. I put this down as false...
  5. X

    Work and friction

    I would assume the normal force is mg x sin theta, but I was told this was incorrect?
  6. X

    Physics: dynamics in a circle

    I think you calculated velocity correctly but you left off the scientific notation. Keep the velocity squared and use that to solve for the acceleration. a = v^2 / r This will give you the answer in m/s^2
  7. X

    Work and friction

    Whis is the minimum work needed to push a 1068 kg car 305 m up a 11.0 degree incline if the effective coefficient of friction is 0.26? I have a hard time understanding why the normal force does not equal mg? How do I find the normal force? Or am I looking at this problem incorrectly?
  8. X

    Calculating mass

    Wow, that easy, huh? Haha, thanks for your help!
  9. X

    Calculating mass

    Astronomers using the Hubble Space Telescope have recently deduced the presence of an extremely massive core in the distant galaxy M87, so dense that it could well be a black hole (from which no light escapes). They measured the speed of gas clouds orbiting the core to be 758 km/s at a distance...
  10. X

    Calculating weight on mars

    How much would someone who has a mass 54.1 kg on Earth weigh if they were to stand on the surface of Mars? (Take RMars= 3393 km and MMars=6.45x10^23 kg. I've been using the formula F=GmM/R^2 with the 3393km converted to meters. (6.67 x 10^-11 Nm^2/kg^2) (54.1 kg) (6.45 x 10^23kg) /...
  11. X

    Finding the coefficient of kinetic friction?

    Thanks for the help! I got the right answer after reading all of your hints, but I'll have to think about it some more to make sense of it.
  12. X

    Finding the coefficient of kinetic friction?

    A force of 45.7 N is required to start a 5.0-kg box moving across a horizontal concrete floor. (a) What is the coefficient of static friction between the box and the floor? (b) If the force continues at the same value, the box accelerates at 0.54 m/s^2. What is the coefficient of kinetic...
  13. X

    Adding force vectors

    Okay, I finally got it! Thanks for the help. :)
  14. X

    Adding force vectors

    I've been given this problem: Two forces act on a block of mass 14.1 kg. The first force has magnitude 28.5 N and is directed along the x axis. The second force has magnitude 6.7 N and is directed at an angle of 38.7 degrees to the x axis. Find (a) the magnitude and (b) the direction (i.e., the...
  15. X

    Horizontal projectile

    Oh, okay. Now it's starting to make more sense. Since the initial velocity is horizontal, then it would be 0.
  16. X

    Horizontal projectile

    For t I got .3656 s. I put 0 in for yo but should v also be 0 if it's the vertical component?
  17. X

    Horizontal projectile

    Okay, I used 9.9 m/s^2 for v and my final answer came to 2.93 m. Does this seem more accurate? I guess I was way off. :x
  18. X

    Horizontal projectile

    I understand that's how to solve the problem, but I still don't think I'm doing this correctly. To calculate the time, I took 186 m/s divided by 68 m and got 2.735 s. Then I plugged the time into the equation y=yo+vyot-1/2gt^2. So it looked like 0+186m/s(2.735s)-1/2(9.8m/s^2)(2.735s)^2. I...
  19. X

    Horizontal projectile

    A hunter aims directly at a small target (on the same level) 68 m away. If the bullet leaves the gun at a speed of 186 m/s, by how much will it miss the target? I just need to know what formula I should use to solve this problem?
  20. X

    Conceptual question

    Shoot! I didn't consider that. Thank you so much for your help!
  21. X

    Conceptual question

    I know that B is incorrect because the speed is slowing down due to gravity. C is also incorrect because the velocity varies when the projectile moves in a parabola. D is incorrect because there is no horizontal component in the acceleration. A is correct because the vertical acceleration is...
  22. X

    Conceptual question

    I'm really bad at these because there are multiple answers and I always leave one out. :grumpy: A projectile is fired from a ship at a distant, floating target. Which of the following statements are true? (There can be more than one correct choice.) a. The vertical component of the...
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