# Standing waves, find distance

nil1996

## Homework Statement

A string of length 1.5m with its two ends clamped is vibrating in fundamental mode. Amplitude at the center of the string is 4mm. Find the distance between the points who have amplitude 2mm.

y=Asinkxcoswt
λ=2*L

## The Attempt at a Solution

First of all i was trying to get the distances of the points from one of the nodes.
so putting t=0 i get y=Asinkx

k=2π/λ
λ=2*L = 2*1.5 = 3

so y= Asin$\frac{2π}{λ}$x
i know the amplitude is 2mm which is half the max amplitude.
$\frac{A}{2}$=Asin$\frac{2π}{λ}$x

So that gives
0.5=sin$\frac{2π}{λ}$x
$\frac{π}{6}$=$\frac{2πx}{λ}$

0.25=x
Now the other partical will be 1.25m from the node.

so the difference is 1m

but the answer given is 50cm
Where i have gone wrong??