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G-Field
PJC P2 Q2
The Moon revolves around the Earth in a
circular motion.
(a) Explain why, on a line joining the centre of
the Earth, E and the centre of the Moon, M,
there is a point X where the resultant
gravitational field strength is zero.
(b) The information related to the Earth and the
Moon is given below.
(i) If the distance EX is 3.4 × 108 m,
determine the distance XM.
(ii) Hence calculate the distance EM.
(iii) Given that the mass of the Earth is 6.0 ×
1024 kg, determine the period of the
Moon’s revolution around the Earth.
G-Field
TJC P2 Q2
(a) Explain what is meant by “the gravitational
potential energy of a body at a point is – 2.5
× 107 J”.
Explain the significance of the negative sign.
(b) (i) A 1000 kg satellite is placed in a circular
polar orbit so that it goes round the
Earth 14 times a day.
(Mass of Earth = 5.97 × 1024 kg)
1. Show that the period of the orbit is
approximately 6170 s.
2. Calculate the radius of the orbit.
(ii) To place the satellite in the orbit, the
satellite is first carried by a rocket which
is launched vertically upwards from
Earth. It is then given a horizontal
impulse when it reaches the correct
altitude. State and explain an advantage
of this vertical launch.
E-Field
TJC P2 Q4
(a) Explain what is meant by the term electric
field strength at a point.
(b)
ABC is a right-angled isosceles triangle. A
positive charge Q is placed each at points
and B while the charge placed at C is
negative and twice the magnitude of that at
the other two points. The electric field
strength at B due to the charge at A is E.
(i) Find, in terms of Q and E, an expression
for the magnitude of the resultant
electric force F experienced by the
charge at point B.
(ii) Indicate on Fig 4.1, the direction of F.
(iii) Fig 4.2 is identical to Fig 4.1. Sketch in
Fig 4.2 the electric field lines around the
three charges.
E-Field
JJC P2 Q3
(a) (i) Define electric potential.
(ii) Distinguish electric potential clearly from
electric potential energy.
(b) A proton is released from rest in a uniform
electric field that has a magnitude of 9.0 ×
104 V m-1. The distance between point A and
point B is 0.60 m
(i) Find the potential difference between
point A and point B.
(ii) Find the change in potential energy of
the proton when it moves from point A to
point B.
(iii) At point A, the speed of the proton is
0.50 × 106 m s-1. Find the speed of the
proton at point B.
(iv) On Fig 3.2, sketch a graph showing how
the electric potential energy of the
proton varies from point A to point B.
(v) On Fig 3.3, sketch a graph showing how
the speed of this proton varies as it
passes from point A to point B.