Question

As Devine rides her bike, she picks up a nail in her front tire. The height, h, of the nail from the ground as she rides her bike over time, t, in seconds, is modelled by the equation below: As Devine rides her bike, she picks up a nail in her front tire. The height, h, of the nail from the ground as she rides her bike over time, t, in seconds, is modelled by the equation below:

f(x)=-14 cos(720(t-10))+14

Using the equation, determine the following. Show your work for part marks.

a) What is the diameter of the bike wheel?

b) How long does it take the tire to rotate 3 times?

c) What is the minimum height of the nail? Does this height make sense? Why?

Answer 1

a) 28 units

b) 0.0262 seconds

c) Minimum height of the nail = 1.923 units

Explanation:

a) From the given equation, f(x) = -14×cos(720(t - 10)) + 14 comparing with the equation for periodic function, y = d + a·cos(bx - c)

Where:

d = The mid line

a = The amplitude

The period = 2π/b

c/b = The shift

Therefore, since the length of the mid line and the amplitude are equal, the diameter of the bike maximum f(x) = -14×-1 + 14 = 28

b) Given that three revolution = 6×π, we have;

At t = 0

cos(720(t-10) = cos(720(0-10)) = cos(7200) = 1

Therefore, for three revolutions, we have

720(t - 10) = 720t - 7200

b = 720

The period = 2π/b = 6·π/720 = 0.0262 seconds

c) The minimum height of the nail is given by the height of the wheel at t = 0, as follows;

f(x) = -14×cos(720(t - 10)) + 14

At t = 0 gives;

f(x) = -14×cos(720(0 - 10)) + 14

Minimum height of the nail = -14×cos(-7200) + 14 = -14×0.863+14 =1.923

Minimum height of the nail = 1.923