02:54
Precalculus: Functions and Graphs
A tidal wave of height 50 feet and period 30 minutes is approaching a sea wall that is 12.5 feet above sea level (see the figure). From a particular point on shore, the distance $y$ from sea level to the top of the wave is given by
$$y=25 \cos \frac{\pi}{15} t$$
with $t$ in minutes. For approximately how many minutes of each 30-minute period is the top of the wave above the level of the top of the sea wall?