Question

Astronaut Mark Kelly and his crew traveled to the International Space Station in the space shuttle. The shuttle burned off all remaining fuel before entering Earth's atmosphere. When the shuttle returned to Earth it landed at a speed of approximately 354 km/hr or 220 mi/hr, about 20 times the landing speed of a commercial aircraft. What accounts for the shuttle's speed upon landing?

Answer 1

A) Earth's atmosphere  

B) initial thrust of take-off  

C) angle of approach upon landing  

D) gravitational potential energy

It would be D. Gravitational potential energy As the shuttle prepares to return to Earth it reduces its speed so that gravity pulls it out of its orbit and toward Earth. As it approaches the earth the gravitational potential energy is converted to kinetic energy. The drag of Earth's atmosphere slows the shuttle's descent and causes some kinetic energy to convert to heat energy.

Answer 2

A couple of things, if the shuttle burned all of it's fuel before entering Earth's atmosphere then that means that the shuttle was accelerating towards Earth until it ran out of fuel.  At that point, there is little to no air resistance (friction) by the lack of an atmosphere so it keeps accelerating  due to Earth's gravitational force.  The closer the shuttle gets to Earth the stronger the gravitational pull the shuttle experiences.  Note that, once the shuttle reaches Earth's atmosphere it will cause significant amount of friction and thus will cause the shuttle to slow down.