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Physics - Energy, Work, and Power

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  • bonkysleuth
    bonkysleuth's Avatar
    276 posts since Mar '07
    • 25 Jun `08, 8:54PM

      A 4.0 kg mass of metal is dropped a distance 0.8m onto the horizontal surface in order to test its hardness.

       

      What is the velocity of the body just before hitting the horizontal surface?

       

      For reference purposes, here are the earlier questions:

       

      (a) when the mass has falen through 0.8m, how much gravitational potential energy has been transformed? [g = 10m/s2]

      Using the mgh formula, you get 32 J

       

      (b) How much kinetic energy does the mass possesss before it hits the horizontal surface?

      I wrote 32 J, similar to the above. Ain't sure what is the velocity so I can't apply the 1/2mv^2 method. I take it that the total energy in the system remains constant - part of the principle of conservation of energy.

       

       

  • wishboy
    wishboy's Avatar
    1,181 posts since Aug '05
    • 25 Jun `08, 9:06PM

      By the principle of conservation of energy,

      Loss in PE = Gain in KE

      mgh = ½mv²

      (10)(0.8) = ½v²

      v² = 16

      v = 4 m/s

  • -*:+:MUSE:+:*-
    -*:+:MUSE:+:*-'s Avatar
    90 posts since Jan '08
    • 29 Jun `08, 1:46PM

      dude cmon. you should be able to solve these problems right away -.-

      practice makes perfect =]

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