Finding fastest point of comet
The comet has the greatest kinetic energy when the force on it is greatest and the gravitational potential energy is smallest
Therefore the greatest kinetic energy is when the comet is closest to the Sun
This is point B; [1 mark]
Why a telescope is fastest near the Earth
The total energy (gravitational potential and kinetic energy) of an object in orbit is conserved: [1 mark]
Gravitational potential energy is proportional to the object’s distance from the surface of the Earth; [1 mark]
Therefore, when an object is closer to the Earth, its gravitational potential energy is lower, so its kinetic energy must be higher: [1 mark]
Kinetic energy is proportional to velocity squared, so if kinetic energy is larger, velocity will also be larger; [1 mark]
