The "Download Now" link directs you to the iTunes App Store, where you must continue the download process. You must have iTunes installed in order to open the link, and you must have an active iTunes account to download the application. This download may not be available in some countries.
From ND Consulting:
Projectile Calculator assists you in calculating values for projectile motion as taught in high school and university/college-level physics courses. This app helps you solve the difficult problems. There is no need to start with initial velocity and angle. Due to Projectile Calculator's advanced calculation engine, you can enter any values you know and Projectile Calculator with compute the rest. For instance, enter a horizontal distance of 80 meters, a vertical displacement of 100 meters and a time of 10 seconds and Projectile Calculator will tell you the initial velocity was 59.6 m/s and was fired at an angle of 82.3 degrees. It will also show you a diagram of the projectile path and tell you when the projectile hit its peak height. This app is an excellent tool for checking your projectile motion homework or playing what-if scenarios by easily changing values of an already-computed calculation. Given its ability to compute answers instantly, students can use it in class to catch mistakes made by the teacher as he/she demonstrates example problems (calculating things slowly using only a calculator). Teachers, use this app to check student answers or use the iPad version as a teaching aid to quickly display diagrams for problem sets. Features: - calculates unknown values from known ones. No need to work top-down, just fill in what you know and Projectile Calculator will calculate the rest - displays diagrams of completed calculations - maintains history of calculations allowing you to go back in time to view old calculations and diagrams and start a new calculation based on a previous one - supports switching between alternate answers in those cases where the calculation results in two solutions - allows you to customize the interface to support the terminology that suits your particular course/preference - iPhone/iPod Touch version supports a compact display option to allow display of all values on one screen, or an expanded view for ease of use while you get familiar with the app - supports "what if" scenarios by allowing you to change any already-calculated value and Projectile Calculator will re-compute the affected values using its heuristic calculation engine - offers individual buttons to clear values you want to force the app to re-compute during the changing of another value - supports various unit systems. It defaults to the metric system, but you can easily convert to another system by merely setting a different value for the acceleration due to gravity in the configuration section - iPad version supports both landscape and portrait displays - displays newly calculated values in blue to distinguish from previously set values