Simple Wave Problem, But I can't figure out the answer

[annakorish]

Please help. I am desperateA string with both ends held fixed in vibrating in its third harmonic. The waves have a speed of 186m/s and a frequency of 250Hz. the amplitude of the standing wave at an antinode is 0.450cm.
A. Calculate the amplitude at point on the string a distance of 15.0 cm fromthe left-hand end of the string
B. How much time does it take the string to go from its largest upward displacement to its largest downward displacement at this point?
C. Calculate the maximum transverse velocity of the string at this point.
D. Calculate the maximum transver acceleration of the string at this point

For this problem, I know how to derive frequency, angular frequency, wavelength, length of the string, etc. but I don't know how to use these info. to solve the problem.

I just need something to start with. I have no idea how to start the problem. Thank a lot.

 

[Cyrus]

Plug these values into the standard wave equation formula.

 

[lightgrav]

At time t = 0 , y_max = A sin ( k x ) , where k = 2 pi / lambda .
Notice that THIS problem uses "sin" since the string is tied down at x=0 (so y=0 there)

That place on the string acts just like an oscillator with amplitude given by y_max . You'll have to find wavelength from speed.

 

[UppityHorse]

Hello.

I am currently working on the same problem for HW. I have every question answered except:

"B. How much time does it take the string to go from its largest upward displacement to its largest downward displacement at this point?"

What is the general technique to solve this problem? Since we want to get from the high peak to the low peak, the distance is twice the amplitude stated in the text of the problem, correct?

Thats where I'm stuck.