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Added GroundToGroundProjectileMotion
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‎src/main/java/com/thealgorithms/physics/GroundToGroundProjectileMotion.java‎

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package com.thealgorithms.physics;
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/**
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* Ground to ground projectile motion calculator
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*
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* Ground to ground projectile motion is when a projectile's trajectory
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* starts at the ground, reaches the apex, then falls back on the ground.
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*
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* @author [Yash Rajput](https://github.com/the-yash-rajput)
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*/
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public class GroundToGroundProjectileMotion {
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private GroundToGroundProjectileMotion() {
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throw new AssertionError("No instances.");
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}
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/** Standard gravity constant (m/s^2) */
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private static final double GRAVITY = 9.80665;
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/**
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* Convert degrees to radians
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*
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* @param degrees Angle in degrees
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* @return Angle in radians
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*/
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private static double degreesToRadians(double degrees) {
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return degrees * (Math.PI / 180.0);
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}
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/**
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* Calculate the time of flight
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*
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* @param initialVelocity The starting velocity of the projectile (m/s)
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* @param angle The angle that the projectile is launched at in degrees
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* @return The time that the projectile is in the air for (seconds)
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*/
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public static double timeOfFlight(double initialVelocity, double angle) {
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return timeOfFlight(initialVelocity, angle, GRAVITY);
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}
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/**
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* Calculate the time of flight with custom gravity
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*
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* @param initialVelocity The starting velocity of the projectile (m/s)
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* @param angle The angle that the projectile is launched at in degrees
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* @param gravity The value used for the gravity constant (m/s^2)
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* @return The time that the projectile is in the air for (seconds)
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*/
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public static double timeOfFlight(double initialVelocity, double angle, double gravity) {
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double viy = initialVelocity * Math.sin(degreesToRadians(angle));
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return 2.0 * viy / gravity;
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}
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/**
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* Calculate the horizontal distance that the projectile travels
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*
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* @param initialVelocity The starting velocity of the projectile (m/s)
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* @param angle The angle that the projectile is launched at in degrees
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* @param time The time that the projectile is in the air (seconds)
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* @return Horizontal distance that the projectile travels (meters)
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*/
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public static double horizontalRange(double initialVelocity, double angle, double time) {
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double vix = initialVelocity * Math.cos(degreesToRadians(angle));
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return vix * time;
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}
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/**
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* Calculate the max height of the projectile
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*
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* @param initialVelocity The starting velocity of the projectile (m/s)
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* @param angle The angle that the projectile is launched at in degrees
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* @return The max height that the projectile reaches (meters)
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*/
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public static double maxHeight(double initialVelocity, double angle) {
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return maxHeight(initialVelocity, angle, GRAVITY);
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}
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/**
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* Calculate the max height of the projectile with custom gravity
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*
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* @param initialVelocity The starting velocity of the projectile (m/s)
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* @param angle The angle that the projectile is launched at in degrees
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* @param gravity The value used for the gravity constant (m/s^2)
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* @return The max height that the projectile reaches (meters)
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*/
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public static double maxHeight(double initialVelocity, double angle, double gravity) {
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double viy = initialVelocity * Math.sin(degreesToRadians(angle));
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return Math.pow(viy, 2) / (2.0 * gravity);
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}
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}

‎src/test/java/com/thealgorithms/physics/GroundToGroundProjectileMotionTest.java‎

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package com.thealgorithms.physics;
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import static org.junit.jupiter.api.Assertions.*;
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import org.junit.jupiter.api.DisplayName;
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import org.junit.jupiter.api.Test;
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/**
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* JUnit test class for GroundToGroundProjectileMotion
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*
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* Contains unit tests for projectile motion calculations using JUnit 5
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*/
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public class GroundToGroundProjectileMotionTest {
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private static final double EPSILON = 0.001; // Tolerance for floating point comparison
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@Test
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@DisplayName("Test time of flight calculation")
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public void testTimeOfFlight() {
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// Arrange
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double initialVelocity = 5.0;
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double angle = 40.0;
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double expectedTimeOfFlight = 0.655;
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// Act
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double flightTimeOutput = GroundToGroundProjectileMotion.timeOfFlight(initialVelocity, angle);
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flightTimeOutput = Math.round(flightTimeOutput * 1000.0) / 1000.0;
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// Assert
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assertEquals(expectedTimeOfFlight, flightTimeOutput, EPSILON, "Time of flight should be " + expectedTimeOfFlight + " seconds");
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System.out.println("Projectile Flight Time Test");
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System.out.println("Input Initial Velocity: " + initialVelocity + " m/s");
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System.out.println("Input Angle: " + angle + " degrees");
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System.out.println("Expected Output: " + expectedTimeOfFlight + " seconds");
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System.out.println("Actual Output: " + flightTimeOutput + " seconds");
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System.out.println("TEST PASSED\n");
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}
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@Test
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@DisplayName("Test horizontal range calculation")
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public void testHorizontalRange() {
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// Arrange
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double initialVelocity = 5.0;
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double angle = 40.0;
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double flightTime = 0.655;
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double expectedHorizontalRange = 2.51;
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// Act
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double horizontalRangeOutput = GroundToGroundProjectileMotion.horizontalRange(initialVelocity, angle, flightTime);
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horizontalRangeOutput = Math.round(horizontalRangeOutput * 100.0) / 100.0;
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// Assert
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assertEquals(expectedHorizontalRange, horizontalRangeOutput, EPSILON, "Horizontal range should be " + expectedHorizontalRange + " meters");
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System.out.println("Projectile Horizontal Range Test");
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System.out.println("Input Initial Velocity: " + initialVelocity + " m/s");
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System.out.println("Input Angle: " + angle + " degrees");
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System.out.println("Input Time Of Flight: " + flightTime + " seconds");
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System.out.println("Expected Output: " + expectedHorizontalRange + " meters");
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System.out.println("Actual Output: " + horizontalRangeOutput + " meters");
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System.out.println("TEST PASSED\n");
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}
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@Test
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@DisplayName("Test max height calculation")
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public void testMaxHeight() {
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// Arrange
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double initialVelocity = 5.0;
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double angle = 40.0;
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double expectedMaxHeight = 0.527; // Updated to match actual calculation
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// Act
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double maxHeightOutput = GroundToGroundProjectileMotion.maxHeight(initialVelocity, angle);
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maxHeightOutput = Math.round(maxHeightOutput * 1000.0) / 1000.0;
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// Assert
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assertEquals(expectedMaxHeight, maxHeightOutput, EPSILON, "Max height should be " + expectedMaxHeight + " meters");
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System.out.println("Projectile Max Height Test");
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System.out.println("Input Initial Velocity: " + initialVelocity + " m/s");
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System.out.println("Input Angle: " + angle + " degrees");
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System.out.println("Expected Output: " + expectedMaxHeight + " meters");
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System.out.println("Actual Output: " + maxHeightOutput + " meters");
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System.out.println("TEST PASSED\n");
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}
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@Test
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@DisplayName("Test time of flight with custom gravity")
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public void testTimeOfFlightWithCustomGravity() {
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// Arrange
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double initialVelocity = 10.0;
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double angle = 45.0;
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double customGravity = 1.62; // Moon gravity (m/s^2)
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// Act
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double flightTime = GroundToGroundProjectileMotion.timeOfFlight(initialVelocity, angle, customGravity);
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// Assert
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assertTrue(flightTime > 0, "Flight time should be positive");
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assertTrue(flightTime > 8.0, "Flight time on moon should be longer than on Earth");
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System.out.println("Custom Gravity Test (Moon)");
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System.out.println("Input Initial Velocity: " + initialVelocity + " m/s");
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System.out.println("Input Angle: " + angle + " degrees");
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System.out.println("Gravity: " + customGravity + " m/s^2");
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System.out.println("Flight Time: " + flightTime + " seconds");
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System.out.println("TEST PASSED\n");
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}
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@Test
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@DisplayName("Test projectile at 90 degrees (straight up)")
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public void testVerticalProjectile() {
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// Arrange
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double initialVelocity = 20.0;
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double angle = 90.0;
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// Act
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double horizontalRange = GroundToGroundProjectileMotion.horizontalRange(initialVelocity, angle, 1.0);
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// Assert
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assertEquals(0.0, horizontalRange, EPSILON, "Horizontal range should be zero for vertical launch");
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System.out.println("Vertical Projectile Test");
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System.out.println("Input Angle: " + angle + " degrees");
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System.out.println("Horizontal Range: " + horizontalRange + " meters");
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System.out.println("TEST PASSED\n");
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}
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@Test
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@DisplayName("Test projectile at 0 degrees (horizontal)")
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public void testHorizontalProjectile() {
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// Arrange
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double initialVelocity = 15.0;
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double angle = 0.0;
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// Act
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double maxHeight = GroundToGroundProjectileMotion.maxHeight(initialVelocity, angle);
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// Assert
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assertEquals(0.0, maxHeight, EPSILON, "Max height should be zero for horizontal launch");
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System.out.println("Horizontal Projectile Test");
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System.out.println("Input Angle: " + angle + " degrees");
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System.out.println("Max Height: " + maxHeight + " meters");
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System.out.println("TEST PASSED\n");
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}
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}

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