Solving Transverse Wave Problems: 25 Hz Frequency, 4.00E-2s Period

[jackleyt]

Homework Statement

Transverse waves on a string have wave speed 8.00 {\rm m/s}, amplitude 0.0700 {\rm m}, and wavelength 0.320 {\rm m}. These waves travel in the x direction, and at t = 0 the x = 0 end of the string is at y = 0 and moving downward.

Find the frequency of these waves: (found: 25.0 Hz)
Find the period of these waves. (found: 4.00 E-2 s)
Write the equation for {y}({x},\:{t}) describing these waves. (Stuck).
Find the transverse displacement of a point on the string at x2 = 0.160 m at time t2= 8.50×10−2 s. (Stuck).

Homework Equations

The Attempt at a Solution

For the third part, this is what I have so far: .07(sin 0)
I don't know if its right. I'm thinking I can probably get the next part if I know what the equation is. Any help? Thanks!

 

[Matterwave]

Do you know the equation for a wave propagating down a string?

y=Asin(kx-wt) what values for A, k, and w would make this work?

 

[jackleyt]

A=.07
K= I'm not sure, but wouldn't x be zero so k would cancel out?
W= i don't know how to go about finding.

 

[Matterwave]

Think about what the equation is saying.

At t=0, the equation says: y=Asin(kx)

So, can you see from there what k should be? Hint: Think about what a wave looks like on that string, and what the y coordinate is for each x coordinate.

Similarly, think at x=0 the equation says y=Asin(wt). what does that say?

 

[jackleyt]

I don't know :/.. is there any other way you could explain it? I'm sorry, it's late and I feel so slow!

 

[jackleyt]

Oh! So I've gotten .07sin(157t-19.6x), but it's telling me it's wrong.??

 

[jackleyt]

Nevermind, got it, thanks!

 

[Matterwave]

no problem =)

 

[jackleyt]

Oh, another question.. for the last part, I'm just plugging and chugging in the numbers to the equation .07sin(-157t+19.6x), and I'm getting -.0124. It says it's wrong. Am i doing something wrong?