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A 64.4-kg skateboarder starts out with a speed of 2.11 m/s. He does 81.6 J of work on himself by pushing with his feet against the ground. In addition, friction does -289 J of work on him. In both cases, the forces doing the work are non-conservative. The final speed of the skateboarder is 8.56 m/s. (a) Calculate the change (PEf - PE0) in the gravitational potential energy. (b) How much has the vertical height of the skater changed? Give the absolute value.

  • Physics - ,

    ΔKE=1/2mvf^2- 1/2mv0^2

    a)Plug numbers in
    1. ΔKE=1/2(64.4)(8.56)^2- 1/2(64.4)(2.11)^2= -2216.05 (because displacement, I think)

    2. -2216.05J+(-289J)-80J
    Answer =-2425.05J

    1. W=ΔKE, W=ΔPE(PE=mgh), ΔPE=ΔKE

    Answer h=3.842m

    Hope this Help

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