Urgent! There is a ferris wheel of radius 30 feet. When the compartments are at their lowest, it is 2 feet off the ground. The ferris wheel makes a full revolution in 20 seconds. Using a cosine function, write an equation modelling the height of time?

Help!
Radius - 30 feet
Lowest point - 2 feet
Time for 1 revolution - 20 seconds
Write cosine function!

1 Answer
Dec 3, 2016

h = -30cos(pi/10t) + 32, {t|t ≥ 0, t in RR}

Explanation:

An equation in cosine is generally of the form y= acos(b(x - c)) + d, where the parameters represent the following:

|a|: the amplitude. When it is negative, it denotes a reflection in the x axis.

(2pi)/b is the period, in this case the length of time it takes for the ferris wheel to come back to its starting point.

c is the phase shift, or the horizontal displacement.

d is the vertical shift

In this case, we can instantly deduce that the period is 20 seconds. We will therefore solve for b.

(2pi)/b = 20

2pi = 20b

b = (2pi)/20

b = pi/10

The amplitude will be given by the formula ("max" - "min")/2. We know the minimum height is 2 feet. Since the radius is 30 feet, the diameter measures 60 feet, and so the highest point is at 62 feet.

The amplitude is therefore (62 - 2)/2 = 60/2 = 30.

The vertical transformation is given by min + amp, or max- amp, which is 2 + 30 = 32.

Finally, due to the nature of the cosine function, the cosine function always starts at a maximum (except when parameter a is negative, in which case it starts at a minimum). I assume that when the time starts, the people are just getting on, so the ferris wheel will be at a minimum. Therefore, a!=30 but instead a!=-30.

Therefore, the equation is h = -30cos(pi/10t) + 32, where h is the height in feet and t is the time in seconds. We finally note the restrictions to be {t|t ≥ 0, t in RR}, because it is impossible to have a negative period of time. The h value will always be positive, so we don't have to restrict that.

Hopefully this helps!