# Boat-man problem, velocity of center of mass

#### Dansuer

1. The problem statement, all variables and given/known data

A man of mass 84.4 Kg is in the back of a boat of mass 425 kg which is moving without friction on ice with velocity 4.16 m/s. the man moves from the back to the top of the boat with velocity 2.08 m/s traveling for 18.2m. How much distance does the boat travel while the man moves?

2. Relevant equations

v$$_{cm}$$ = (v$$_{1}$$m$$_{1}$$ + v$$_{2}$$m$$_{2}$$)/(m$$_{1}$$+m$$_{2}$$)

3. The attempt at a solution

The way i try to solve this was that i put V$$_{cm}$$ = 0 because i choose a coordinate system with velocity V$$_{cm}$$. The equation on top gives the velocity of the boat to be 0.41 m/s. Subtract this to the velocity of the boat relative to the ice gives v=3.7 m/s
Now i calculated the distance travelled: 18.2 : 2.08 = x : 3.7 which is 32.37

but it's not the same results as the book gives as a solution. What did i do wrong?

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#### cupid.callin

why are you taking the frame at velocity of CM. take frame at v=0
then you dont need to find the relative speeds, just use them as given

#### Dansuer

You're right i could've done that. But the answer to the problem does not change. And it's not the same as the book. Is the book wrong or i am ?

#### cupid.callin

I need to sleep now ... its 3AM here ...

But you can post your answer and i'll tell you your mistake as soon as i wake up.
will that work?

#### Dansuer

of course, no hurry You can find my answer in the point 3 of my first post

thanks

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