how can i activate strokeWeight(random(10));
only when ball touches left or right side of the rectangle?

1. float diam=100;
   float a=0;
   
   void setup(){
    size(500,400);
   background(0);
   noFill();
    
   }
   
   void draw(){
   background(0);
   
   float x=sin(a)*width/2;
   float y=height/2;
   float x1=width/2;
   float y1=height/2;
   float d=dist(x,y,x1, y1);
   
   strokeWeight(1);
   stroke(255,255,0);
   //line(width/2,0,width/2+x,y);
   fill(255);
   ellipse(width/2+x,height/2,20,20);
   
   noFill();
   if (d<50){
     strokeWeight(random(10));
    
   }
   else {
     strokeWeight(1);
    
   }
   
   stroke(0,255,0);
   rectMode(CENTER);
   rect(x1,y1,50,50);
   a+=0.05;
   }