1. Limited time only! Sign up for a free 30min personal tutor trial with Chegg Tutors
    Dismiss Notice
Dismiss Notice
Join Physics Forums Today!
The friendliest, high quality science and math community on the planet! Everyone who loves science is here!

Heat, Work & Internal Energy

  1. Jan 9, 2010 #1
    1. The problem statement, all variables and given/known data

    Please help with this problem!
    How many sprints from rest to a speed of 4.5 m/s would a 59 kg woman have to complete in order to burn off 5.0 x 102 Calories? (Assume 100% efficiency in converting food energy to mechanical energy.)

    2. Relevant equations



    3. The attempt at a solution

    Speed (v) = 4.5 m /s
    .
    ==> h = v2 / 2g = (4.5)2 / ( 2 * 9.8) = 1.033 m
    .
    Mass (m) = 59 kg
    .
    Energy (E) = 5.0 * 10-2 cal = 5.0 * 10-2 cal * (1000 * 4.186) J
    .
    = 209.3 J
    .
    number of sprints is :
    .
    n = E / 2 m g h
    .
    = (20.9.3 J) / ( 2 * 59 * 9.8 * 1.033 )
    .
    = 0.1752 sprints
     
  2. jcsd
  3. Jan 9, 2010 #2
    Have you tried calculating the kinetic energy the woman would have, converting it to calories, and finding the number of sprints? I'm not sure if that will get you the right answer, but I come up with about 3.5 sprints. You may want to check the back of the book to see if that is close.
     
  4. Jan 10, 2010 #3

    Redbelly98

    User Avatar
    Staff Emeritus
    Science Advisor
    Homework Helper

    Is the energy to be burned off 5.0x10+2 or 5.0x10-2 ?

    Legion81 is correct, you'll need to figure out the kinetic energy of the sprinter.
     
Know someone interested in this topic? Share this thread via Reddit, Google+, Twitter, or Facebook




Similar Discussions: Heat, Work & Internal Energy
Loading...