一題物理既問題

Coin A and coin B are floating on the same water surface.

Coin A takes 2 s to rise 8 cm from its lowest position to its highest position.

So, 8 cm is the amplitude of the water wave,

and 2 s is the time elapsed for half of wave-length

So, for one complete vibration of the coin, 2 X 2 = 4 s is needed.


Also, the wave takes 6 s to travel from A to B.

So, after 6 s from the beginning, coin B starts to oscillate, and it takes another 4 s for the complete vibration.

Therefore, time required for coin B to complete one complete vibration from the beginning

= 6 + 4

= 10 s

The frequency at A = B

The time take for A complete 1/2 cycle = 2s

1 period = 4s

Time for 1 complete cycle for A and B are 4s.


PS: The wave takes 6s to travel, and take 4s to finish vibration.
The total time need = 6 + 4 = 10s.