Balloon Cart with Proportional Deceleration

#include <AFMotor.h>    //Adds Motor shield library

#define trigPin 7
#define echoPin 6  

float v;
int duration;
long distance;
long distance1;
long distance2;

AF_DCMotor motor(1);

void setup() {
  Serial.begin(9600);
  pinMode(trigPin, OUTPUT);
  pinMode(echoPin, INPUT);

  motor.setSpeed(200);
  motor.run(RELEASE);
}

void loop() {
  do{
  distance = (duration/2) /29.1; 
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(1000);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance = (duration/2) /29.1;
  Serial.print("distance ");
  Serial.print(distance);
  Serial.println("cm");
  }while(distance <= 4 || distance > 40);

 do{
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(1000);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance1 = (duration/2) /29.1;
  Serial.print("distance1 loop ");
  Serial.print(distance1);
  Serial.println("cm");
  delay(100);
  v = ((float)distance1/(distance+1))*255;
  Serial.print("speed ");
  Serial.println(v);
  motor.run(FORWARD); 
  motor.setSpeed(v);
  Serial.println("Forward");
 }while(distance1 > 5);

motor.run(RELEASE);
motor.setSpeed(0);
delay(3000);

do{
  digitalWrite(trigPin, HIGH);
  delayMicroseconds(1000);
  digitalWrite(trigPin, LOW);
  duration = pulseIn(echoPin, HIGH);
  distance2 = (duration/2) /29.1;
  Serial.print("distance2 loop 2 ");
  Serial.print(distance2);
  Serial.println("cm");
  Serial.println("Backward");
  motor.run(BACKWARD);
  motor.setSpeed(150);
}while(distance2 <= 19);
motor.run(RELEASE);
delay(3000);
}