# Math Help - trigonometry word question?

1. ## trigonometry word question?

A ferry pontoon in a tidal river is attached to the river edge by a jetty 20 metres long. The jetty is hinged to the bank so that the pontoon can move up and down with the tides.At the highest tide, the jetty is horizontal. There is a difference of 2.15 metres between the highest and lowest tides experienced in the river at this point.

1. Through what angle must the jetty hinge be able to turn?
2. How far from the river bank (horizontally) is the pontoon at the low tide mark?

2. ## Re: trigonometry word question?

Originally Posted by starr17
A ferry pontoon in a tidal river is attached to the river edge by a jetty 20 metres long. The jetty is hinged to the bank so that the pontoon can move up and down with the tides.At the highest tide, the jetty is horizontal. There is a difference of 2.15 metres between the highest and lowest tides experienced in the river at this point.
It's best to draw a picture:

We can now see that

$\sin\theta = \frac{2.15}{20}$.

And once we find $\theta$, we can find the horizontal distance $d$ from the pontoon at low tide to the bank with

$\cos\theta = \frac d{20}$.