The general equation of the sine function is
d = Asin(b(t -c)) +h
Here, A is amplitude, `(2pi)/b` is the period, c is the phase shift and h is the vertical shift.
Since the diameter of the wheel is 18 feet, the amplitude is A = 18/2 = 9. Since the highest point is 16 feet above water surface is 16 feet, the vertical shift is determined by d = 16 = A + h = 9 +h.
h = 16 - 9 =7.
Since the wheel completes a revolution every 10 seconds, the period of the sine function is 10. Then,
`(2pi)/b = 10` and `b=(2pi)/10 = pi/5`
Finally, since it took 4 seconds to reach 16 ft, we can find c:
`16 = 9*sin(pi/5(4 - c)) + 7`
`sin(pi/5)(4-c) = 1`
`pi/5(4-c) = pi/2`
`4-c = 2.5` and c = 1.5
So the equation of sine wave will be
`d=9sin(pi/5(t-1.5)) + 7`