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Average force exerted by the ball

  1. Oct 11, 2007 #1
    1. The problem statement, all variables and given/known data

    A baseball (m = 145 g) traveling 35 m/s moves a fielder's glove backward 15 cm when the ball is caught. What was the average force exerted by the ball on the glove?
    Magnitude

    2. Relevant equations

    -(1/2)mv^2

    3. The attempt at a solution

    (1/2)(145)(35)^2=-88812.5
     
  2. jcsd
  3. Oct 11, 2007 #2

    PhanthomJay

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    you have calculated the kinetic energy lost. The problem asks for the force. What equation(s) might you use to solve for F?
     
  4. Oct 11, 2007 #3
    F=(1/2)kx^2
     
  5. Oct 11, 2007 #4
    Be careful with your calculations - baseball m = 145 g ...
     
  6. Oct 11, 2007 #5

    PhanthomJay

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    No, you're fishing in the wrong pool! Are you familiar with energy methods, or kinematics and Newton 2?
     
  7. Oct 11, 2007 #6
    would the equation just be F=mv?
     
  8. Oct 11, 2007 #7

    PhanthomJay

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    You mean F=ma, don't you? So how would you calculate 'a' knowing that the ball goes from 35m/s to a stop in a 15cm distance? (Hint: use the kinematic equation that relates distance with acceleration and velocity change, and watch your units.
     
  9. Oct 11, 2007 #8
    Vf^2=Vi^2*a*d
     
  10. Oct 11, 2007 #9
    0=1225+2*a*.15
    -2*a*.15=1225
    a*.15=-612
    a=-4083.3
     
  11. Oct 12, 2007 #10

    PhanthomJay

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    Yes that looks good, don't forget units of a is m/sec^2. What does the minus sign tell you? Now plug it into F=ma to solve for F, watch units, and interpert the significance of the minus sign.
     
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