1. The problem statement, all variables and given/known data The planet T is a planet of mass M and radius R, and very thin atmosphere (no air resistance). A rail gun has been mounted on the surface of T at the North Pole. A projectile of mass m is fired form the rail gun with an unknown speed vo at an unknown angle θ with respect to the local horizontal. The projectile is observed to rise to a maximum height above the surface of ¼ R. At this maximum height the projectile has a speed of 75.0 m/s. If M=1.5 x 10^20 (such that GM=1.0 x 1010 Nm2/kg) and R=200km, find vo in m/s. and the launch angle θ. 2. Relevant equations F=ma F=(GMm)\R^2 ma=(GMm)\R^2 a=(v^2)\r 3. The attempt at a solution I know that F=ma, and Gravitational F=(GMm)\R^2 so ma=(GMm)\R^2 , a in rotational is a=(v^2)\r , so I would set m((v^2)\R)=(GMm)\R^2 . Yet is v in this equation the one they want? In finding the θ once I found the v would there be components in the x and y direction? Can I find it that way? Thank you very much for the help.