# Questions of this style

1. Aug 10, 2013

4a) An oil drop of mass 3.3 x 10-15 kg falls vertically, with uniform velocity, through the air between two vertical parallel plates with zero potential difference that are 3.0 cm apart. Explain this motion.

(b) When a potential difference of 2.0 x 103 V is applied between the plates, the drop is observed to move with uniform velocity at an angle of 45o to the vertical. Explain this result, with a diagram, indicating the forces acting on the drop, and calculate the charge on the drop.

(c) The path of the drop suddenly changes, becoming inclined at 18.43o to the vertical. Subsequently the path changes again and is inclined at 33.70o to the vertical. Explain these results.
Deduce from these observations the best estimate of the elementary unit of charge.

(d) The plates are now arranged horizontally, 12 mm apart, with no potential difference. A drop of oil, mass 10-14 kg, is observed to fall vertically with constant velocity of 4.0 x 10-4 ms-1. When a pd of 1.5 kV is applied to the plates the drop rises vertically with a velocity of 8.0 x 10-5 ms-1. How many electrons are present in the drop?

The drop experiences air resistance proportional to its velocity

6a) If the radius of the Earth RE = 6.38 x 103 km and g = 9.81 ms-2 is the acceleration of free fall, obtain an expression for the minimum launch speed required to put a satellite into polar orbit, over the poles, and calculate its magnitude.

(b) What is the ratio of the minimum launch speed required to put a satellite into polar orbit, over the poles, to the minimum launch speed for an equatorial orbit, around the equator, when they are in close Earth orbits?

(c) What minimum initial speed must a space probe have if it is to leave the gravitational field of the Earth?

(d) What minimum launch speed is required for a probe to hit the Sun? Neglect the Earth’s gravitational field.

(e) Ignoring the Earth’s gravitational field, what minimum launch speed is required for a probe to leave the solar system?

Distance of the Earth from the Sun, RES = 1.50 x 108 km
Mass of the Sun, MS = 1.99 x 1030 kg
Mass of the Earth, ME = 5.98 x 1024 kg

What I want to ask is, what books or websites will give me good practice for solving problems of this style? What websites cover the necessary theory in good detail? (my knowledge of mechanics is fine but other than that recommendations would be good) I have I.E. Irodov's problems but I don't know if they cover the classes of problem being asked here (e.g. orbits around a rotating body).