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B Force, mass, acceleration, kinetic energy

  1. Feb 22, 2017 #1


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    Hi all,

    I stumbled into a somewhat odd mathematical problem, so I guess I've overlooked an important detail.
    If I have a mass of 1kg on wheels horizontally, and apply 10N of constant force so the mass is accellerating. I assume the velocity of that mass after 1 second is approx 10m/s. Then kinetic energy should be approx 50 Joule. (1/2 (m*v*v)).

    Then I have a mass of 10kg on wheels horizontally, and apply 10N of force for one second. Maybe I'm dumb, but it appears to me that the kinetic energy after one second is only 5 Joule. Shouldn't it be 50 Joule?

    What have I missed out?

    Br. Vidar
  2. jcsd
  3. Feb 22, 2017 #2


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    Work is force times distance, not force times time. The 10 kg doesn't move so far in 1 s.

    Try the same thing with momentum instead of energy, and surprise yourself :rolleyes: !
  4. Feb 22, 2017 #3


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    Yeah! Sometimes I stumble in my own brain. Thanks for clearing this up :-)
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