Answer:
(D) It is equal to the original velocity of the skater.
Explanation:
The velocity of the center of mass of a system is

The velocity of the center of mass is constant if there is no external force, because the total momentum of the whole system is conserved.
So, before the snowball is thrown, the velocity of the center of mass is equal to that of the skater. This velocity will always be equal to the velocity of the center of mass of the system.
Answer:
0.36s, 2.3s
Explanation:
Let gravitational acceleration g = 9.81 m/s2. And let the throwing point as the ground 0 for the upward motion. The equation of motion for the rock leaving your hand can be written as the following:

where s = 4 m is the position at 4m above your hand.
is the initial speed of the rock when it leaves your hand. g = -9.81m/s2 is the deceleration because it's in the downward direction. And t it the time(s) it take to get to 4m, which we are looking for


t = 2.3 or t = 0.36
The answer is D. All of the above
Compression and rarefraction, the other guy's answer it's wrong