This question involves the concepts of the law of conservation of momentum.
The magnitude of the final momentum of the eight ball is "0.22 N.s".
According to the law of conservation of momentum:

where,
= initial momentum of the cue ball = 0.23 N.s
= initial momentum of the eight ball = 0 N.s (since ball is initially at rest)
= final momentum of the cue ball = 0.01 N.s
= final momentum of the eight ball = ?
Therefore,

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Answer:
2.When they reach the bottom of the fall
Explanation:
The potential energy of the waterfall is maximum at the maximum height and decreases with decrease in height. Based on the law of conservation of mechanical energy, as the potential energy of the water fall is decreasing with decrease in height of the fall, its kinetic energy will be increasing and the kinetic energy will be maximum at zero height (bottom of the fall).
Thus, the correct option is "2" When they reach the bottom of the fall
(a) Period of the wave
The period of a wave is the time needed for a complete cycle of the wave to pass through a certain point.
So, if an entire cycle of the wave passes through the given location in 5.0 seconds, this means that the period is equal to 5.0 s: T=5.0 s.
(b) Frequency of the wave
The frequency of a wave is defined as

since in our problem the period is

, the frequency is

(c) Speed of the wave
The speed of a wave is given by the following relationship between frequency f and wavelength

: