Question

Homework-2 – Working with a class. Problem: Attached with this homework is code for a class called DroppedObject. This class is used to to store the state of a falling object. The problem this class/object can be used to solve is detailed below. Your task for this homework is to read and understand the attached class. Note this class is formatted like all classes should be with private variables, constructors, a toString method, getter and setter methods, and other relevant methods. Write a main program that will use the class to solve the problem described below. Run your resulting program for a height of 100 feet. Upload to blackboard a copy of your main java class and a screen shot of your output. This is the problem: Write a program to simulate a falling object. The program should ask for the initial height of the object, in feet. The output of the program should be the time for the object to fall to the ground, and the impact velocity, in ft/s and miles/hour. Your program should use Euler’s method to numerically solve the differential equations describing the motion of a falling object. In Euler’s method, the state of the object at some small future time is calculated using the values at the present time. This small future time step is typically called delta time, or dt. Thus the position (p) and speed (v) of the object in the next timestep t + dt is written as a simple function of the position and speed at the current time step t (g is the acceleration due to gravity): v(t+dt) = v(t) + g * dt p(t+dt) = p(t) + v(t+dt) * dt You should actually start out with the velocity as zero, and the position at the initial height of the object. Then your position (above the ground) would be: p(t+dt) = p(t) - v(t+dt) * dt And you would integrate until the position becomes less than or equal to zero. The input/output formats for your program should look like this: Program to calculate fall time and impact speed of a falling object dropped from a specific height. Enter initial height in feet: 100 Falling time = 2.492224 seconds Impact speed = 80.249613 feet/sec Impact speed = 54.715645 mph Part of this assignment is to determine an optimum value for dt. Clearly, the value of the time step that you use in the simulation will be important. If the timestep (dt) is too large, then the results will not be accurate. However, if the time step is too small, then the program run time will be excessive. For this assignment, you must determine the value of delta time that is as large as possible but at the same time, results in an answer that is accurate to 5 significant figures – i.e., further decreases in the time step no longer change the result past the 5 th digit to the right of the decimal place. Turn in your program configured with this value of dt. Accuracy and precision is important for this assignment. You should use a double float data type for all real numbers. Also assume the effect of gravity does not vary with distance from the earth, the rate of acceleration is 32.2 feet per second per second, and the resistance of passing through the atmosphere is non-existent. Using symbolic constants for gravity G = 32.2 and delta time DT = .000??????? makes sense.

public class DroppedObject 
{
//
// Description: This class keeps the state of a falling object. The state means the height above the ground, the current 
// vertical velocity, the gravity constant , and the time differential (delta t).
// This class will contain methods to update the state of the object, print and set the state variables of the falling object
//
// Written by George Cardwell 
// Written as an example for CSC-202 Class Fall 2017.
        
        
// Private state variables

        private  double altitude;
        private double deltatime;
        private double velocity;
        private double gravityconst;
        private double TimeOfFlight = 0.0;
        
        
        
//  methods
        // consturctors
        
        public DroppedObject()
        {
                altitude = 0.0;
                deltatime = 0.0;
                velocity = 0.0;
                gravityconst = -32.2;
        }
        
        public DroppedObject(double h,double v, double dt, double g)
        {
                altitude = h;
                velocity = v;
                deltatime = dt;
                gravityconst = -g;
        }
        
//
// state Methods
//
        public void UpdateState()
        {
                velocity = velocity + gravityconst*deltatime;
                altitude = altitude + velocity*deltatime;
                TimeOfFlight = TimeOfFlight + deltatime;
        }
//
//      Getters and setters
//
        public double getAltitude() {
                return altitude;
        }

        public void setAltitude(double altitude) {
                this.altitude = altitude;
        }

        public double getDeltatime() {
                return deltatime;
        }

        public void setDeltatime(double deltatime) {
                this.deltatime = deltatime;
        }

        public double getVelocity() {
                return velocity;
        }

        public double getVelocityMPH(){
                return velocity * (3600.00/5280.00);
        }
        public void setVelocity(double velocity) {
                this.velocity = velocity;
        }

        public double getGravityconst() {
                return gravityconst;
        }

        public void setGravityconst(double gravityconst) {
                this.gravityconst = gravityconst;
        }
        
        public double getTimeOfFlight()
        {
                return TimeOfFlight;
        }

        @Override
        public String toString() {
                return "DroppedObject [altitude=" + altitude + ", deltatime=" + deltatime + ", velocity=" + velocity
                                + ", gravityconst=" + gravityconst + ", TimeOfFlight=" + TimeOfFlight + "]";
        }
        
}

public class DroppedObject 
{
//
// Description: This class keeps the state of a falling object. The state means the height above the ground, the current 
// vertical velocity, the gravity constant , and the time differential (delta t).
// This class will contain methods to update the state of the object, print and set the state variables of the falling object
//
// Written by George Cardwell 
// Written as an example for CSC-202 Class Fall 2017.
        
        
// Private state variables

        private  double altitude;
        private double deltatime;
        private double velocity;
        private double gravityconst;
        private double TimeOfFlight = 0.0;
        
        
        
//  methods
        // consturctors
        
        public DroppedObject()
        {
                altitude = 0.0;
                deltatime = 0.0;
                velocity = 0.0;
                gravityconst = -32.2;
        }
        
        public DroppedObject(double h,double v, double dt, double g)
        {
                altitude = h;
                velocity = v;
                deltatime = dt;
                gravityconst = -g;
        }
        
//
// state Methods
//
        public void UpdateState()
        {
                velocity = velocity + gravityconst*deltatime;
                altitude = altitude + velocity*deltatime;
                TimeOfFlight = TimeOfFlight + deltatime;
        }
//
//      Getters and setters
//
        public double getAltitude() {
                return altitude;
        }

        public void setAltitude(double altitude) {
                this.altitude = altitude;
        }

        public double getDeltatime() {
                return deltatime;
        }

        public void setDeltatime(double deltatime) {
                this.deltatime = deltatime;
        }

        public double getVelocity() {
                return velocity;
        }

        public double getVelocityMPH(){
                return velocity * (3600.00/5280.00);
        }
        public void setVelocity(double velocity) {
                this.velocity = velocity;
        }

        public double getGravityconst() {
                return gravityconst;
        }

        public void setGravityconst(double gravityconst) {
                this.gravityconst = gravityconst;
        }
        
        public double getTimeOfFlight()
        {
                return TimeOfFlight;
        }

        @Override
        public String toString() {
                return "DroppedObject [altitude=" + altitude + ", deltatime=" + deltatime + ", velocity=" + velocity
                                + ", gravityconst=" + gravityconst + ", TimeOfFlight=" + TimeOfFlight + "]";
        }
        
}

Answer 1

//DropeedObject.java

package com.test;

import java.util.Scanner;

public class DroppedObject
{
//
// Description: This class keeps the state of a falling object. The state means the height above the ground, the current
// vertical velocity, the gravity constant , and the time differential (delta t).
// This class will contain methods to update the state of the object, print and set the state variables of the falling object
//
// Written by George Cardwell
// Written as an example for CSC-202 Class Fall 2017.
  
  
// Private state variables

private double altitude;
private double deltatime;
private double velocity;
private double gravityconst;
private double TimeOfFlight = 0.0;
  
  
  
// methods
// consturctors
  
public DroppedObject()
{
altitude = 0.0;
deltatime = 0.0;
velocity = 0.0;
gravityconst = -32.2;
}
  
public DroppedObject(double h,double v, double dt, double g)
{
altitude = h;
velocity = v;
deltatime = dt;
gravityconst = -g;
}
  
//
// state Methods
//
public void UpdateState()
{
velocity = velocity + gravityconst*deltatime;
altitude = altitude + velocity*deltatime;
TimeOfFlight = TimeOfFlight + deltatime;
}
//
// Getters and setters
//
public double getAltitude() {
return altitude;
}

public void setAltitude(double altitude) {
this.altitude = altitude;
}

public double getDeltatime() {
return deltatime;
}

public void setDeltatime(double deltatime) {
this.deltatime = deltatime;
}

public double getVelocity() {
return velocity;
}

public double getVelocityMPH(){
return velocity * (3600.00/5280.00);
}
public void setVelocity(double velocity) {
this.velocity = velocity;
}

public double getGravityconst() {
return gravityconst;
}

public void setGravityconst(double gravityconst) {
this.gravityconst = gravityconst;
}
  
public double getTimeOfFlight()
{
return TimeOfFlight;
}
public void setTimeOfFlight(double time)
{
TimeOfFlight += time;
}

@Override
public String toString() {
return "DroppedObject [altitude=" + altitude + ", deltatime=" + deltatime + ", velocity=" + velocity
+ ", gravityconst=" + gravityconst + ", TimeOfFlight=" + TimeOfFlight + "]";
}
  
}

//Main.java

package com.test;

import java.util.Scanner;

public class Main

{

public static void main(String[] args) {

Scanner sc = new Scanner(System.in);

System.out.print("Enter initial height in feet:");

int height = sc.nextInt();

//v(t+dt) = v(t) + g * dt p(t+dt) = p(t) - v(t+dt) * dt

DroppedObject dp = new DroppedObject(0.0, 0.0, 0.4142, 32.2);

while(Math.abs(dp.getAltitude()) < height)

{

dp.UpdateState();

//System.out.println("Altitude is :"+dp.getAltitude());

}

System.out.println("Falling time = "+Math.abs(dp.getTimeOfFlight()) + " seconds Impact Speeed = "+Math.abs(dp.getVelocity()) + " feet/sec Impace Speed = "+ Math.abs(dp.getVelocityMPH()) + "MPH");

//Falling time = 2.492224 seconds Impact speed = 80.249613 feet/sec Impact speed = 54.715645 mph

}

}

//output: