Friday, October 12, 2007

Scribe Post (BRYAN L.)

Today in class...
We continued off working on the bicycle question. Jeng's foot was on the pedal ranging from 8cm to 30cm from the ground as she pedalled. We already drew the graph (or should've), and had figured out the sine and cosine equations for the graph. Today we had to figure out how long Jeng's right foot is 20cm or higher, per cycle.

One of our classmates did an excellent job at solving the question, but had difficulty with finding out the second 20cm point on the graph. After a short discussion and explaination by Mr.K, we concluded that with the first 20cm point already found; 1.6618;
we had to take (pi) - 1.6618 = 1.2798
then (pi) + 1.2798 = 4.6214

And to varify that 4.6214 is indeed in quad. 3 (which it's suppose to be because you can tell by looking at the graph that the 20m point is before 2.25s, which marks the end of quad. 3, being 3/4 of the cycle), (pi)(1.5)=4.7124 and 4.6214 is clearly less than that.

So then you take theta which = 4.6214 and you put it in the formula theta = 2(pi) / 3 because that's what you let theta equal while solving the equation; f(t)= -11cos(2(pi) x) + 19 .
So 4.6214 = [2(pi) /(3)] x
multiply both sides by [(3)/(2(pi)]
and 2.2065 = x

The last step is taking 2.2065 - 0.7935 which is the first value of theta (and the correct one) that our fellow classmate had figured out. So the final answer is that Jeng's foot was 20m or higher off the ground for 1.4131 seconds per cycle.

The last portion of Thursday's class, we were put into groups by numbers. We were given a sheet per group called "Ferris Wheel" or something (I don't have the sheet so I don't know the exact title). There were four questions (A thru D) which talked about the height and time of the ferris wheel. It is a practice of what we have just newly learned. The questions were as follows:

A) Write two equations, one sine and one cosine, that would represent the distance above the ground as a function of time. Let t = 0 when the seat is at the lowest point on the wheel.

B) How high will a person be 10 seconds after they begin riding the Ferris wheel?

C) How long after a person gets on the ride will they actually be 100 feet in the air?

D) How long, during each revolution, is a person more than 60 feet in the air?

The answers are to be published by one person from each group to represent the whole group. Good luck on the assignment!

The Scribe for Monday's class will be Cheyenne T.

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