# Another Trig question (sine wave)

1. Jun 2, 2009

### Imperil

During a strong wind, a tall building, such as the CN Tower, can sway back and forth as much as 100 cm, with a period of 10s.

b) Write an equation for this function, in the form y = a sin kx

2Pi / k = 10
10k = 2Pi
k = Pi/5

y = 100sin(Pi/5)x

Now my question is regarding the wording of the question. It says that it can sway back and forth as much as 100 cm but does not state if that is the diameter or radius. Am I correct in thinking it is referring to the radius?

Or would the correct answer be: y = 50sin(Pi/5)x because it swings 50 cm each way? Sorry to ask such a stupid question I'm just not 100% sure what it is asking.

2. Jun 2, 2009

### dx

I'm pretty sure they mean 100cm is the 'radius' (properly called the amplitude of vibration).

3. Jun 2, 2009

### HallsofIvy

Staff Emeritus
Specifically, because of the wording "back and forth", I agree with dx. 100 cm "back" and 100 cm "forth" is 100 cm in each direction. If it had simply said "sways 100 cm" then I would think "50 cm in each direction".

(I actually started to disagree with dx, then reread the statement!)

4. Jun 2, 2009

### Imperil

Great thanks so much for the help guys I really appreciate it :)