A sled of mass m is coasting on the icy surface of a frozen river. While it is p

Question

A sled of mass m is coasting on the icy surface of a frozen river. While it is passing under a bridge, a package of equal mass m is dropped straight down and lands on the sled (without causing any damage). The sled plus the added load then continue along the original line of motion. How does the kinetic energy of the (sled + load) compare with the original kinetic energy of the sled? A) It is 1/4 the original kinetic energy of the sled. B) It is 1/2 the original kinetic energy of the sled. C) It is 3/4 the original kinetic energy of the sled. D) It is the same as the original kinetic energy of the sled. E) It is twice the original kinetic energy of the sled.

Explanation / Answer

conservation of momentum m*v1=(m+m)*v2 v2=v1/2 ke1=0.5*m*v1^2 ke2=0.5*2m*v2^2 ke2/ke1=2*(v2/v1)^2=2*1/4=1/2 ke2=(1/2)*ke1 B) It is 1/2 the original kinetic energy of the sled.

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