# ferris wheel..

• Mar 30th 2011, 06:58 PM
helpy
ferris wheel..
a)a ferris wheeel has a diameter of 22m, and is 1m higher than the ground at its lowest point. the wheel completes one revolution every 15 minutes, write a cosine equation h(t) representing the height a chair is off the ground in metres, as a function of time in minutes, if the chair start at the lowest point.

b) write in sine equation.

c)from a height of 18m or higher, you can see your grandma's house. from how long each revolution can you see your grandms's house. (use the cosine equation)

need some help here guys. Thanks in advance.(Happy)
• Mar 31st 2011, 08:49 AM
Dagger2006
Think about what the normal trig function would look like. In part a, looks something like:

h(t)=Acos (mt- h) + k where A is amplitude, m adjusts the speed of rotation, h shifts left and right, and k is the height.

Remember that cos (t)=1 at the highest point, and cos (t) = -1 at the lowest point. Then just play around with the number till you get it to work out correct.
• Mar 31st 2011, 09:12 AM
helpy
yeah, I kinda get it, but I would like to know the answer so I know i did it correctly... but thnx
• Mar 31st 2011, 09:16 AM
TheEmptySet
Then post your work! We would be happy to see if it is correct!
• Mar 31st 2011, 10:57 AM
helpy
a) h(t)= 11 cos 2pi/15 t+1 is that correct guys?
• Mar 31st 2011, 11:18 AM
TheEmptySet
Quote:

Originally Posted by helpy
a) h(t)= 11 cos 2pi/15 t+1 is that correct guys?

I am sorry to say that your answer is incorrect. Pleae check the intial condions!

$h(0)=11\cos(0)+1=12$ this is a bit odd.

Hint: find the circular function first. Find a cosine funtion such that $f(0)=0$ and $\displaysytle f\left(\pi\right)=22$

Now shift this up by one unit
• Mar 31st 2011, 11:37 AM
helpy
Quote:

Originally Posted by TheEmptySet
I am sorry to say that your answer is incorrect. Pleae check the intial condions!

$h(0)=11\cos(0)+1=12$ this is a bit odd.

Hint: find the circular function first. Find a cosine funtion such that $f(0)=0$ and $\displaysytle f\left(\pi\right)=22$
Now shift this up by one unit

HUmmmm.. im really not getting it, can you please show me instead?
• Mar 31st 2011, 11:49 AM
TheEmptySet
Quote:

Originally Posted by helpy
HUmmmm.. im really not getting it, can you please show me instead?

That would really defeat the point of you understanding this!

As per the hint to start you need a cosine fuction such that

$f(x)=0$ and $f(\pi)=22$

What shifts can you use to accomplish this?
• Mar 31st 2011, 12:39 PM
helpy
am i missing phase shift?
• Mar 31st 2011, 12:43 PM
TheEmptySet
Quote:

Originally Posted by helpy
am i missing phase shift?

I have no idea! You still have not shown your work!
• Mar 31st 2011, 12:47 PM
helpy
11cos2pi/15(t-7.5)+1

like this? omg, the hints didnt help lol.
• Apr 2nd 2011, 11:23 AM
Dagger2006
With the work you showed, if you plug in pi you will not get 22. f(pi) = 11 cos [(2pi/15)(pi-7.5)] +1 yeilds you getting a pi^2 when you distribute. You might want to try to avoid that.

P.S I know it is frusterating not getting the answer. But think of this, in your math classes, teachers usually show you how to do most of the problems. Yet, when you try them yourself most of us have trouble doing it correctly the first few times. This is why it's so important not to be told the entire answer and to figure it out yourself.