Momentum Surfboard Walking

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  • #1
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Homework Statement


A 32 kg boy is standing on a 59 kg raft that is 8 m wide. He walks 6 m from a point 1.0 m from the left edge of the raft to a point 1.0 m from the right edge of the raft. If you ignore resistance of the water to the motion of the raft, how far does the raft move during this procedure


Homework Equations



F=ma
p=mv

No idea

The Attempt at a Solution



i draw a force diagram for it and looks like the one that will effect the movement of the boat is

F = friction force
but I have no idea what the friction constant is. and also will the mass affect the movement of the boat?

and I also dont have any velocity to use the equation of

m1v1 + m2v2 = m3v3
32(v1) + 0 = 91(v3)
 

Answers and Replies

  • #2
PeterO
Homework Helper
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Homework Statement


A 32 kg boy is standing on a 59 kg raft that is 8 m wide. He walks 6 m from a point 1.0 m from the left edge of the raft to a point 1.0 m from the right edge of the raft. If you ignore resistance of the water to the motion of the raft, how far does the raft move during this procedure


Homework Equations



F=ma
p=mv

No idea

The Attempt at a Solution



i draw a force diagram for it and looks like the one that will effect the movement of the boat is

F = friction force
but I have no idea what the friction constant is. and also will the mass affect the movement of the boat?

and I also dont have any velocity to use the equation of

m1v1 + m2v2 = m3v3
32(v1) + 0 = 91(v3)

This is just a centre of mass question. The centre of mass of the system will remain stationary. The c of m of the two components moves. Where will they each finally be?
 
  • #3
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This is just a centre of mass question. The centre of mass of the system will remain stationary. The c of m of the two components moves. Where will they each finally be?
x1 = (m1x1 + m2x2) / (m1+m2)
91(1) + 91(7) / (182)
x1 = 4m

uhmm i believe i did something wrong :confused:
 
  • #4
PeterO
Homework Helper
2,426
48
x1 = (m1x1 + m2x2) / (m1+m2)
91(1) + 91(7) / (182)
x1 = 4m

uhmm i believe i did something wrong :confused:
suddenly the boy and raft have become 91 kg each???
 
  • #5
41
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suddenly the boy and raft have become 91 kg each???
x1 = (m1x1 + m2x2) / (m1+m2)
x1 = (32(1) + 59(4)) / (91)
x1 = 2.725

x1 = (m1x1 + m2x2) / (m1+m2)
x1 = (32(7) + 59(4)) / (91)
x1 = 5.055

x = 5.055 - 2.725
x = 2.33m

but it's wrong, I'm confused where my error is
 
Last edited:
  • #6
41
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nvm, it was just a miscalculation, i got it now, thank you :)
 

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