text: # Magnitude of average force
  
  1. Mar 1, 2009
  
  ### Crichar1
  
  A woman with a mass of 44 kg runs at a speed of 8 m/s and jumps onto a giant 30 kg skateboard initially at rest. What is the combined speed of the woman and the skateboard?
  
  44 kg / 8 m/s=5.5
  30 kg / 8m/s=3.75
  
  5.5+3.75=9.25m/s
  
  2. Mar 1, 2009
  
  ### The Bob
  
  What do you know about mechanics that will help? Any equations?
  
  The Bob
  
  3. Mar 1, 2009
  
  ### Freyster98
  
  Think momentum.
  
  4. Mar 1, 2009
  
  ### Crichar1
  
  i tried the linear momentum equation..mass * velocity and the answer was still incorrect
  
  5. Mar 1, 2009
  
  ### The Bob
  
  But what did you do to get this incorrect answer?
  
  The Bob
  
  6. Mar 1, 2009
  
  ### Crichar1
  
  mass x velocity
  
  44kg x 8m/s= 352
  
  30kg x 8m/s=240
  
  352-240=112m/s
  
  didn't seem right but i thought i would try it anyways
  
  7. Mar 1, 2009
  
  ### The Bob
  
  Right, now I see what you're doing. Have you heard of something called 'conservation of momentum'? Basically, the momentum before a 'change' must be equal to the combined momentum afterwards. You've, therefore, wrongly assumed that the skateboard has velocity of 8ms-1.
  
  So... try imagining the woman and the skateboard as one mass after they have 'combined'.
  
  The Bob
  
  8. Mar 1, 2009
  
  ### Freyster98
  
  Conservation of momentum. The total momentum before she jumps on the board=total momentum after she jumps on the board.
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