# Wave speed and time question

1. Jun 23, 2010

### hartfan

1. The problem statement, all variables and given/known data
A wave is moving through a string at 450 m/s. The wavelength is 0.18 m and the amplitude is 2.0 mm. What is the time required for a particle on the string to move through 1.0 km? (The answer given is 5.0x10 s).

2. Relevant equations
The only equations I can think of are the ones relating frequency, period, wave speed and wavelength, where wave speed = wave length x frequency. The period is the inverse of frequency.

3. The attempt at a solution
If I divided the 1.0 km by the wave speed, I get 2.22 s. I don't know how else the 1.0 km is related to anything else, and can't figure out how the amplitude has to do with anything. How do you even find the function of the wave? This has been bothering me for almost a week now and I've been looking up every physics text I can find in the library and none of them could offer me a solution. Please help. Thanks.

2. Jun 23, 2010

### Staff: Mentor

Don't mix up the motion of the wave itself--governed by that speed = wave length X frequency formula--with the motion of the particles of the string. The wave moves along the string, but which way do the particles of the string move? That's where the amplitude (and the frequency) comes in.

3. Jun 23, 2010

### hartfan

Wow. I finally get it now. Thanks for the brilliant tip. I don't know why I never thought of it that way before.