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NotTim

  • 3 years ago

Determine the magnitude of the apparent weight of a 56 kg student standing in an elevator when the elevator is experiencing an acceleration of (a) 3.2 m/s^2 downward and (b) 3.2 m/s^2 upward.

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  1. bahrom7893
    • 3 years ago
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    W = m*a When it's going up, acceleration is: g+a, when it's going down acceleration is g-a

  2. bahrom7893
    • 3 years ago
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    a) total a = -9.8-3.2 = -13 W = 56*(-13)N

  3. NotTim
    • 3 years ago
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    You see, here's what I did for a and b.

  4. bahrom7893
    • 3 years ago
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    b) total a = -9.8 + 3.2 = -6.6 W = 56*(-6.6)N

  5. NotTim
    • 3 years ago
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    a) f=ma =(56)(3.2+9.81) =728.56N

  6. NotTim
    • 3 years ago
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    Why is the force negative in both cases?

  7. bahrom7893
    • 3 years ago
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    because weight is pushing down.

  8. NotTim
    • 3 years ago
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    Ok. Give me a second to redo this...

  9. bahrom7893
    • 3 years ago
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    same thing, just change the signs

  10. bahrom7893
    • 3 years ago
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    you found the normal force, which has the same magnitude, but opposite direction

  11. NotTim
    • 3 years ago
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    And its alright if my signs are negative? Because the answers are A) 3.7*10^2N and b) 7.3*10^2N

  12. bahrom7893
    • 3 years ago
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    ohh yea they asked for magnitude. If they just asked for weight, ur answers wld be negative

  13. bahrom7893
    • 3 years ago
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    since weight has magnitude and direction. In this case it's going down, hence the negative.

  14. NotTim
    • 3 years ago
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    k. ill work with this. if i need help, ill call out

  15. NotTim
    • 3 years ago
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    Hey @bahrom7893 ?

  16. bahrom7893
    • 3 years ago
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    hey

  17. NotTim
    • 3 years ago
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    the answer for A) was wrong. you probably explained this, but i forgot

  18. NotTim
    • 3 years ago
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    We got -728.56N. The book says 3.7*10^2N

  19. bahrom7893
    • 3 years ago
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    Wait in the answer, is the answer for a greater than the answer for b?

  20. NotTim
    • 3 years ago
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    No.

  21. bahrom7893
    • 3 years ago
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    A) 3.7*10^2N and b) 7.3*10^2N Aren't those the answers?

  22. NotTim
    • 3 years ago
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    yup

  23. bahrom7893
    • 3 years ago
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    oh yea.. obv. Hang on I know what we did wrong

  24. NotTim
    • 3 years ago
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    for A), i did this: "56)(-3.2-9.81)

  25. bahrom7893
    • 3 years ago
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    well it makes sense.. i just always confuse the signs of g. g has to be positive in this case.

  26. NotTim
    • 3 years ago
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    would that make my value of 3.2N positive too?

  27. bahrom7893
    • 3 years ago
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    http://www.intuitor.com/student/elevatorrProblem.php

  28. bahrom7893
    • 3 years ago
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    it's the sign of g, i always get confused with it..

  29. NotTim
    • 3 years ago
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    am I to consider 3.2N a positive or negative force?

  30. bahrom7893
    • 3 years ago
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    well is it pushing down or up?

  31. NotTim
    • 3 years ago
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    It's pushing down

  32. NotTim
    • 3 years ago
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    If it was -ve, it would make sense mathematically, but not in terms of real world physics(for me)

  33. bahrom7893
    • 3 years ago
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    then it's negative, but they're just asking for magnitude, or abs value of that force.

  34. NotTim
    • 3 years ago
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    ok. give me a moment to readi guess

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