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Please Help, Another Energy and Momentum

  1. Jun 24, 2012 #1
    1. The problem statement, all variables and given/known data
    A construction worker at the top of a ladder drops her 250 g hard hat from a height of 22m. When it reaches the ground it is traveling at 9.0 m/s. What was the average fore of friction as it fell.



    2. Relevant equations
    Stuck here....


    3. The attempt at a solution
    Can't figure out what equations to use.... Tried finding t, then using ft=mv and solving for t, but that does work.
     
  2. jcsd
  3. Jun 24, 2012 #2
    Use the work energy theorem.
     
  4. Jun 24, 2012 #3
    Would you mind explaining buddy, kinda lost...
     
  5. Jun 24, 2012 #4
    W = ΔEk + ΔEp

    W is work due to friction.
    ΔEk is the change in kinetic energy.
    ΔEp is the change in gravitational potential energy.

    In this case, the hat gains kinetic energy but loses potential energy, so ΔEk is positive, and ΔEp is negative.
     
  6. Jun 24, 2012 #5
    KK I got that, but how would I go on to finding the force of friction?
     
  7. Jun 24, 2012 #6
    W = F x d, you know what d is.
     
  8. Jun 24, 2012 #7
    O I see now, so solving for F would give you the average force. True, thanks buddy mind taking a look at my other thread? Title is Momentum + Energy :)
     
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