# Thread: New Senior Math Simple Harmonic Motion Question

1. ## New Senior Math Simple Harmonic Motion Question

Hi, in the New Senior Math 4 unit textbook, in question 14 they get 12.47 pm, however I am continuously getting 11:32.5 am.

The question is as follows:
The deck of a ship is 2.4 m below the level of a wharf at low tide and 0.6 m above wharf level at high tide. Low tide is a 8:30 am and high tide is at 2:35 pm. Find the time when the deck is level with the wharf, assuming the motion of the tides is simple harmonic.

2. ## Re: New Senior Math Simple Harmonic Motion Question

I get 12:47pm.

Here is my working.

Attachment 34010

3. ## Re: New Senior Math Simple Harmonic Motion Question

Originally Posted by harrowed2
I get 12:47pm.

Here is my working.

Attachment 34010
Good effort.

You can also do it this way:

Period T = 730 mins. Amplitude = 1.5m
.: T = 2pi/n = 730 mins ==> n = 2pi/730.

x = -1.5 cos (nt)

At wharf level, x = 0.9 m = -1.5 cos(2pi/730 t) ==> 2pi/730 t = pi - inverse cos (0.9/1.5) = 0.70483 .. pi

.: t = 257.2639 .. mins = 4 hrs 17.26 mins

.: deck at wharf level at 8.30 + 4.1726 .. = 12.47pm

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