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.

Answer 1

Answer:B

Explanation:

Given

mass of Sled is m

another package of mass m is thrown on it

Suppose u be the initial velocity of sled

conserving momentum

$mu=2mv$

$v=\frac{u}{2}$

where v is the final velocity

Initial kinetic energy $=\frac{1}{2}mu^2$

Final Kinetic Energy$=\frac{1}{2}(2m)\cdot (\frac{u}{2})^2$

Final Kinetic Energy$=\frac{1}{2}\times \frac{1}{2}mu^2$

Final kinetic Energy is half of initial