2.12(物理：求出跑道长度)假设飞机的加速度是a而起飞速度是v，那么可以使用下面的公式计算出飞机起飞所需的最短跑道长度： 跑道长度 = v ^ 2 ÷ (2 × a)
编写程序，提示用户输入以米 / 秒 (m / s)为单位的速度 v 和以米 / 秒的平方(m / s^2)为单位的加速度a，然后显示最短跑道长度。 下面是一个运行示例: Enter speed and acceleration:60 3.5 The minimum runway length for this airplane is 514.286
2.12(Physics: finding runway length) Given an airplane’s acceleration a and take-off speed v, you can compute the minimum runway length needed for an airplane to take off using the following formula: length = v ^ 2 ÷ (2 × a)
Write a program that prompts the user to enter v in meters/second (m/s) and the acceleration a in meters/second squared (m/s2), then, displays the minimum runway length. Here is a sample run: Enter speed and acceleration:60 3.5 The minimum runway length for this airplane is 514.286
参考代码：
package chapter02; import java.util.Scanner; public class Code_12 { public static void main(String[] args) { double RunwayLength,AirplaneAcceleration,AirplaneSpeed; System.out.print("Enter speed and acceleration:"); Scanner AirSpeedAccelInput = new Scanner(System.in); AirplaneSpeed = AirSpeedAccelInput.nextDouble(); AirplaneAcceleration = AirSpeedAccelInput.nextDouble(); RunwayLength = Math.pow(AirplaneSpeed, 2) / (2 * AirplaneAcceleration); System.out.println("The minimum runway length for this airplane is " + RunwayLength); AirSpeedAccelInput.close(); } } 结果显示： Enter speed and acceleration:60 3.5 The minimum runway length for this airplane is 514.2857142857143 Process finished with exit code 0