Answer:
d = 6 sin(2Ï€/7 t + 3Ï€/2)
Step-by-step explanation:
Equation for simple harmonic motion is:
d = A sin(2Ï€/T t + B) + C
where A is the amplitude,
T is the period,
B is the horizontal shift (phase shift),
and C is the vertical shift.
Given that A = 6, T = 7, and C = 0:
d = 6 sin(2Ï€/7 t + B)
At t = 0, the buoy is at d = -6:
-6 = 6 sin(2Ï€/7 (0) + B)
-1 = sin(B)
3Ï€/2 = B
d = 6 sin(2Ï€/7 t + 3Ï€/2)
Notice you can also use cosine instead of sine and get a different phase shift.
d = 6 cos(2π/7 t + π)
You can even use phase shift properties to simplify:
d = -6 cos(2Ï€/7 t)
Any of these answers are correct.