Physics
Gravitational and electric potentials
- 1.
Outside a spherical planet the gravitational field at radius R is 8.0 N kg^-1. Find the field at 2R and the ratio of potential there to potential at R, taking potential zero at infinity.
[3 marks] · no calculator - 2.
A charge +3.00 microcoulomb moves slowly from potential 20.0 V to 80.0 V. Find its change in electric potential energy and work done by the electric field.
[3 marks] - 3.
A satellite orbits a spherical planet at radius 7.00e6 m from its centre. GM = 3.99e14 m^3 s^-2. Find circular orbital speed and period, ignoring other bodies, to 3 significant figures.
[3 marks] - 4.
Two point charges +2.00 microcoulomb and -2.00 microcoulomb are 0.400 m apart in vacuum. Find potential and electric field at their midpoint. Use k = 8.99e9 N m^2 C^-2.
[3 marks] - 5.
A spherical planet has surface radius R = 6.00e6 m and surface g = 10.0 m s^-2. Find minimum surface launch speed to reach radius 3R with zero speed there. Ignore atmosphere and rotation. Compare with escape speed, to 3 significant figures.
[3 marks] - 6.
Point charges +Q at x = 0 and +4Q at x = 0.600 m lie in vacuum, Q > 0. Find the finite point on the x-axis where net field is zero and explain why net potential is not zero there with zero at infinity.
[3 marks]
Marking points are indicative, not an official mark scheme. Accept equivalent valid methods and supported interpretations that address the task; award each mark once without requiring the model wording.