Field Theory Answers

State in words, Newton’s law of Gravitation.

By considering the centripetal force which acts on a planet in a circular orbit, show that T²  is directly proportional to R³ , where T is the time taken for one orbit around the Sun and R is the radius of the orbit.

A planet has radius 3/2 that of the earth and a density of 1/3 that of the earth. If a man jumps 1.5m on the earth, the approximate height he might jump on the planet is?

Calculate the least kinetic energy which must be given to a mass of 2000kg at the earth's surface for the mass to reach a point distance Ro from the center of the earth. Ignore the effect of the earth's rotation. 

A communication satellite occupies an orbit such that its period of revolution about the earth is

24hrs. Explain the significance of this period

Define gravitational potential.

Derive its expression at the earth's surface and show that its value here is approximate -63MJkg-1.

(i.) State Newton's law of gravitation. Give the meaning of any symbol you use.

Define the terms gravitational field and gravitational field strength.

Use your answers in (i) and (ii) to show that the magnitude of the gravitational field strength at the earth's surface is F GM where M is the mass of the earth, R is the radius of the earth and G is the gravitational constant.

The base of a mountain is at sea level where the gravitational field strength is 9.810N/kg. The value of the gravitational field strength at the top of the mountain is 9.790N/kg. Calculate the height of the mountain above the sea level.

A rectangular 40-loop coil, 10cm x 12cm, carrying a current of 2A is in the vicinity of an external magnetic field. This external magnetic field has the same magnitude as that set up at the centre of an 800-loop circular coil (32cm in diameter) carrying a current of 80A. What will be the maximum torque experienced by the rectangular coil?

A spring has a force constant of B0 N/m, it vibrates with a frequency of 7 Hz. Calculate the,

a) period;

b) angular frequency:

c) mass of the spring,

How far apart are two charges , one of magnitude is 3 uC and the other magnitude is 5uC if the force between them is 20N