Posted by help on Monday, November 29, 2010 at 6:34pm.
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.
i read the question wrong..thank for the help
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