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Babynini

  • one year ago

Work and Force.

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  1. Babynini
    • one year ago
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    A car drives 800ft on a road that is inclined 9 degrees to the horizontal. The car weighs 2700lb. Thus gravity acts straight down on the car with a constant force. F=-2700j. Find the work done by the car in overcoming gravity. You are expected to use vectors and the appropriate formula to find work.

  2. rational
    • one year ago
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    |dw:1433491777790:dw|

  3. rational
    • one year ago
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    Force : F = <0, -2700> Displacement : s = <800cos(9), 800sin(9)> yes ?

  4. Babynini
    • one year ago
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    yep yep.

  5. Babynini
    • one year ago
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    what's that j thing? that would be just the other angle there? 81?

  6. rational
    • one year ago
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    i : unit vector along horizontal direction (x axis) j : unit vector along vertical direction (y axis)

  7. rational
    • one year ago
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    F=-2700j is same as F= 0i - 2700j

  8. Babynini
    • one year ago
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    right right.

  9. Babynini
    • one year ago
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    so now?

  10. Babynini
    • one year ago
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    w = f *d ?

  11. rational
    • one year ago
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    simply take the dot product for work done \[W = F\bullet s \]

  12. rational
    • one year ago
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    W = F.s = <0, -2700> . <800cos(9), 800sin(9)> = ?

  13. Babynini
    • one year ago
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    337898.445

  14. rational
    • one year ago
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    what happened to the negative sign

  15. Babynini
    • one year ago
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    ..it didn't want to be there xD *-337898.445

  16. Babynini
    • one year ago
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    the work is negative?

  17. rational
    • one year ago
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    Yes the work done by gravity is negative so, the work done by the car will be positive : +337898.445

  18. Babynini
    • one year ago
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    Fabulous. That makes sense :) thank you soo much!

  19. rational
    • one year ago
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    yw:)

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