We got rocket 200km above see level. Horizontal speed is zero. So, it eventually fell on Earth. We will lunch rocket horizontally. What the final speed it will reach? Pegasus-3 Gross Mass: 985 kg. Empty Mass: 203 kg. Thrust (vac): 3,525 kgf. Isp: 293 sec. Burn time: 65 sec. Propellants: Solid Isp(sl): 240 sec. Diameter: 1.0 m. Span: 1.0 m. Length: 2.1 m. Country: USA. Should be enough data. If you provide an equation, how you figure out speed, it will be greatly appreciated(so I can calculate speed for different types of rockets). Sorry, not a rocket scientist (tried google, but felt). Excuse my English.