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anonymous

  • one year ago

A 0.145 kg baseball is thrown horizontally at 15 m/s from a platform, so that it starts at 5.2 m above the ground. How much has its kinetic energy increased when it reaches the ground? 16 J , 24 J , 0 J , or 7.4 J ? :/

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  1. Michele_Laino
    • one year ago
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    the initial kinetic energy is: \[KE = \frac{1}{2}m{v^2} = \frac{1}{2} \times 0.145 \times {15^2} = ...Joules\]

  2. anonymous
    • one year ago
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    so we get 16.3125? so our solution is 16 J?

  3. Michele_Laino
    • one year ago
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    that result is right! Nevertheless it is not our final answer!

  4. anonymous
    • one year ago
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    ohh okay! what is netx?

  5. Michele_Laino
    • one year ago
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    we have to consider that situation: |dw:1433103218745:dw| our ball, in free falling, has gained a vertical velocity

  6. anonymous
    • one year ago
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    yes:)

  7. Michele_Laino
    • one year ago
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    now, we have to compute that vertical speed

  8. anonymous
    • one year ago
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    ok! how do we do taht?

  9. Michele_Laino
    • one year ago
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    such vertical speed is given by the so called formula of Torricelli, which is: \[v = \sqrt {2gh} = \sqrt {2 \times 9.81 \times 5.2} = ...m/\sec \]

  10. anonymous
    • one year ago
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    10.10006 ? what happens now? :O

  11. Michele_Laino
    • one year ago
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    ok! Now we have this situation: |dw:1433103512624:dw|

  12. Michele_Laino
    • one year ago
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    namely the final velocity has the subsequent magnitude: \[{v_f} = \sqrt {{{10}^2} + {{15}^2}} = ...m/\sec \]

  13. anonymous
    • one year ago
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    18.0277?

  14. Michele_Laino
    • one year ago
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    ok! So the final kinetic energy is: \[KE = \frac{1}{2}m{v^2} = \frac{1}{2} \times 0.145 \times {18^2} = ...Joules\]

  15. anonymous
    • one year ago
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    okay! we get 23.49 so about 24 J is our solution?

  16. Michele_Laino
    • one year ago
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    no, since that the requested energy change is: \[\Delta KE = 23.49 - 16 = ...Joules\]

  17. anonymous
    • one year ago
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    ohh okay so we get 7.49 so about 7.4 J is our answer? :O

  18. Michele_Laino
    • one year ago
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    yes! that's right!

  19. anonymous
    • one year ago
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    yay!! thanks@!!

  20. Michele_Laino
    • one year ago
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    :)

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