Physics help!

[misstoi21]

The mass of a boat is M=80kg, the mass of a boy is m=36kg. The boy moves from the stern to the bows of the boat. What distance does the boat move, if its length is 2.8m? At such low speeds the water resistance may be neglected. Hint: Center of mass remains at rest.

Please help becuase I am stumped... :confused:

[cookiemonster]

You just posted this!

http://www.physicsforums.com/showthread.php?p=171839#post171839

cookiemonster

[himanshu121]

M_{boat} \Delta {X_{boat}} + m_{boy}\Delta {X_{boy}} =0

Coose ur reference frame let it be at the bow of the boat
Now dboy=dboy/boat+dboat

Let x be the displacement of boat then (Delta)Xboat = x
then
dboy = x-l

Where l is the length