physics
A 70.8 kg man is standing on a frictionless ice surface when he throws a 2.3 kg book at 10.5 m/s. With what speed does the man move across the ice as a result?
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The speed at which the man moves across the ice as the result of throwing the book is the same as the speed he threw the book, 10.5 m/s. This is due to the fact that the momentum of the man (before throwing the book) plus the momentum of the book (after being thrown) remains the same (because momentum is conserved). The man's initial momentum was zero (as he was stationary on the ice) so the momentum of the book upon being thrown simply provides the total momentum and hence the velocity of the man across the ice.
