A 60.0 kg girl stands up on a stationary floating raft and decides to go into shore. She dives off the 180 kg floating raft with a velocity of 4.0 m/s [W]. Ignore the substantial friction real objects in water experience. What is the momentum of the girl as she is diving? What is the momentum of raft as the girl is diving? What is the final speed of the raft just after the girl dives?

Question

anonymous · Answer

Momentum is given by:$$p=mv$$where p is momentum; m is mass; and v is velocity.  That should give you a big hint as to how to find the girls momentum.  

Linear momentum of a system is conserved.  For the system in question that conservation of momentum is expressed by:$$p _{sys}=p _{sys}^{'}$$where psys is the momentum of the system before the girl dives in; and p'sys is the momentum of the system after the girl dives in.  We can expand that and get:$$m _{sys}v _{sys}=m _{girl}v _{girl}+m _{raft}v _{raft}$$where mays is the mass of the girl plus the mass of the raft; vsys is the velocity of the system; and the other variables are self explanatory.  Note that the problem states that the raft is stationary before the girl dives in, so that should be a big hint as to what vsys is.

anonymous · Answer

Do you see how to solve the problem, now?

anonymous · Answer

Would the momentum of the raft as the girl's jumping off be zero?

anonymous · Answer

yes it will be zero

anonymous · Answer

she dives horizontally,
with a momentum m v and the raft will have an equal and opposite momentum M V = -m v  because just before the dive the total momentum was zero for both objects.

anonymous · Answer

from the above given equation written by Psisquared,  The momentum on left side become zero. and the 2nd  term of right side becomes equal and opposit to the 1st term of right side...

anonymous · Answer

That's what I thought. Thanks so much :)