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What is her speed relative to the ice surface?

  • Thread starter Ry122
  • Start date
  • #1
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A 44 kg girl is standing on a plank that has a mass of 170 kg. The plank, originally at rest, is free to slide on a frozen lake, which is a flat, frictionless supporting surface. The girl begins to walk along the plank at a constant speed of 1.37 m/s relative to the plank.
What is her speed relative to the ice surface?

My attempt:
The horizontal force the girl exerts on the plank is f=1.37(44)=60.28N
so the speed of the plank relative to the ice should be 60.28=170a a=.354ms
and her speed relative to the ice should be 1.37-.354=1.016
but this is incorrect, what am i doing wrong?
 

Answers and Replies

  • #2


The horizontal force the girl exerts on the plank is f=1.37(44)=60.28N
Here's at least one error in your thinking: How can a force be a speed times a mass?
 
  • #3
565
2


where do i begin then?
 
  • #4
565
2


would momentum be involved?
 

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