Which of the following best explains why the minimum speed needed to escape from…
PHYSICS · Single correct · A Level · Physics · Fields and their consequences · Fields and their consequences
Problem
Which of the following best explains why the minimum speed needed to escape from Earth is greater than the speed needed for a circular orbit at the same altitude?
(a) Escape motion experiences significant air resistance, so extra speed above orbital speed is needed to compensate for the energy lost while climbing through the atmosphere.
(b) Escape velocity must overcome the combined gravitational pull of Earth, Moon and Sun, whereas a circular orbit considers Earth’s gravity alone.
(c) Escape requires the total mechanical energy to become zero, whereas a circular orbit requires the total energy to remain negative.
(d) When calculating escape velocity the centripetal force supplied by gravity is not counted, so an additional speed term is added beyond the circular orbital speed.