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I need help in these problems please

  1. Feb 12, 2007 #1
    How do you do these problems:

    1) What is the magnitude of the force required to accelerate an electron of mass 9.1x10^-31 kg from rest to a speed of 2.0x10^7 m/s for a distance of 0.5 cm

    (a) 1.8 x 10^-21 N
    (b) 9.0 x 10^-19 N
    (c) 1.8 x 10^-16 N
    (d) 3.6 x 10^-14 N

    2) In an elevator system, a motor rotates a shaft wrapping or unwrapping a chain that raises or lowers the elevator car. The car's mass is 1.20x10^3 kg and is designed to carry a maximum load of 9.5x10^2 kg. While in motion, a constant frictional force of 3.5x10^4 N acts on the car.

    (a) What power must the motor deliver to raise the fully loaded car at a speed of 2.5 m/s?

    (b) The elevator system is modified by connecting a free-hanging 5.0x10^2 kg counterweight to the chain that passes over the shaft of the motor, as shown below. What power must the motor now deliver to raise the fully loaded car at a speed of 2.5 m/s?

    Thank you very much
     
    Last edited: Feb 12, 2007
  2. jcsd
  3. Feb 12, 2007 #2

    cristo

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    Welcome to PF, KraYzie. Please note that for homework problems, we ask you to show your work before we can help you.

    Do you have any thoughts on the questions?
     
    Last edited: Feb 12, 2007
  4. Feb 12, 2007 #3
    for #1 I used W = Fd. I changed the .5cm to .005m but i quite cannot get the answer.

    I have no clue about #3 :(
     
    Last edited: Feb 12, 2007
  5. Feb 12, 2007 #4

    cristo

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    This isn't showing your working; it is a stating one brief point. How do you intend to use work to solve this problem?
    Well, to start with, do you know any equations relating power and force?
     
  6. Feb 12, 2007 #5
    yeah I know P = W/T

    for #2, I have this answer written down which is C but I don't know how I got it because I just punched numbers into the calculator omg I'm so screwed
     
  7. Feb 13, 2007 #6
    can somebody really help me? I have been trying since yesterday. Please
     
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