Q2.4 This question is about a probe in orbit. A probe of mass m is in a circular orbit of radius r around a spherical planet of mass M. (a) State why the work done by the gravitational force during one full revolution of the probe is zero. 1 (b) Deduce for the probe in orbit: (i) speed v (ii) total energy E (c) It is now required to place the probe in another circular orbit further away from the planet. To do this, the probe's engines will be fired for a very short time. State and explain whether the work done on the probe by the engines is positive, negative or zero.

Q2.4 This question is about a probe in orbit. A probe of mass m is in a circular orbit of radius r around a spherical planet of mass M. (a) State why the work done by the gravitational force during one full revolution of the probe is zero. 1 (b) Deduce for the probe in orbit: (i) speed v (ii) total energy E (c) It is now required to place the probe in another circular orbit further away from the planet. To do this, the probe's engines will be fired for a very short time. State and explain whether the work done on the probe by the engines is positive, negative or zero.