Posted by help on Monday, November 29, 2010 at 6:34pm.
A 45.00 kg child standing on a frozen pond throws a 0.60 kg stone to the east with a speed of 5.80 m/s. Neglecting friction between child and ice, what is the speed (in m/s) of the child after throwing the stone?
I'm kind of confused about the masses..

physics  drwls, Monday, November 29, 2010 at 7:00pm
What confuses you about the masses?
They they you what they are.
Total momentum is conserved and remains zero.
That means the stone and the child, after the stone is thrown, have equal and opposite momenta.
45*Vchild = 0.6*Vstone = 3.48 kg m/s
Vchild = 3.48/45 = ____ m/s
The minus sign means the child goes backwards, relative to the thrown stone direction. Since that only ask for the speed, you can forget about the minus sgn. 
physics  help, Monday, November 29, 2010 at 7:18pm
i read the question wrong..thank for the help