Term-2 Quiz 2_LO2 and 3 Answer Key
Grade/Cluster
11 ES
Subject
Physics Advanced
Section
Date
Name
Duration 25 mins
ID
Score/20
NOTE: Use where required;
Me = Mass of the earth= 5.98x1024 kg,
Re = radius of the Earth= 6.37x106 m,
G = Universal Gravitational constant= 6.67x10-11 Nm2/kg2.
I-Choose the best answer
[5 marks, 1 each]
1. A ball is falling toward the ground. Which of the following statements is true?
D.
The force that the ball exerts on Earth is equal in magnitude to the force that
Earth exerts on the ball.
The ball undergoes the same acceleration as Earth.
The magnitude of the force the Earth exerts on the ball is greater than the
magnitude of the force the ball exerts on the Earth.
The force gives a lesser acceleration to the small mass of the ball.
E.
All of the above
A.
B.
C.
2. A planet has two moons with identical mass. Moon 1 is in a circular orbit of radius r. Moon 2 is
in a circular orbit of radius 2r. The magnitude of the gravitational force exerted by the planet
on Moon 2 is
A.
Four times as large
B.
Twice as large
C.
The same
D.
Half as large
E.
One-fourth as large as the gravitational force exerted by the planet on Moon 1
T1-SWQ
Page 1 of 4
G11-Core-Physics
3. A satellite moves in a circular orbit at a constant speed around Earth. Which of the following
statements is true?
A.
No force acts on the satellite
B.
The satellite moves at constant speed and hence doesn’t accelerate.
C.
The satellite has an acceleration directed away from Earth.
D.
The satellite has an acceleration directed toward Earth.
E.
Work is done on the satellite by the force of gravity.
4.
The figure above shows a planet in an elliptical orbit about the Sun. In a given period Δt, the
planet moves from point (A) to (B). On the opposite side of its orbit, the planet moves from point
(C) to point (D) in the same amount of time, Δt. Which of the following statement is not true?
A.
The object is moving slower from A to B.
B.
The object is moving with the same speed throughout.
C.
The object is moving faster from C to D.
D.
The area swept between AB is the same as that between CD.
E.
The force of gravity on the planet is more when it is closer to the sun.
5.
T1-SWQ
Page 2 of 4
G11-Core-Physics
The figure shows a satellite in orbit around the Earth. Its motion is independent of
A.
The mass the Earth.
B.
The mass of the Satellite.
C.
The radius of the orbit.
D.
The mass of the Earth as well as the radius of the orbit.
E.
None of the above.
II- Solve the following problems
[10 marks]
1. A 600-kg satellite is in a circular orbit about Earth at a height above Earth equal to Earth’s
mean radius. Find
a. The gravitational force acting on it
𝐺𝑚𝑀 6.67 × 10−11 × 600 × 5.98 × 1024
𝐹𝑔 = 2 =
= 1.47 × 103 𝑁
(2 × 6.37 × 106 )2
𝑟
b. The period of its revolution,
𝑇=√
4𝜋 2 𝑟 3
4𝜋 2 × (2 × 6.37 × 106 )3
=√
= 14306𝑠
𝐺𝑀
6.67 × 10−11 × 5.98 × 1024
2. An object of mass 0.50 kg is transported to the surface of Planet X where the object's
weight is measured to be 20 N. The radius of the planet is 4.0  106 m.
a. What is the mass of planet X?
Fgr 2 20 ´ (4.0 ´10 6 )2
GmM
Fg = 2 Þ M =
=
= 9.6 ´10 24 kg
-11
r
GM 6.67´10 ´ 0.5
b. What free fall acceleration will the 0.50-kg object experience when transported to a
distance of 2.0  106 m from the surface of this planet?
g=
T1-SWQ
GM 6.67 ´10-11 ´ 9.6 ´10 24
=
=17.8m / s 2
2
6
6 2
r
(4.0 ´10 + 2.0 ´10 )
Page 3 of 4
G11-Core-Physics
3. Two moons orbit a planet in nearly circular orbits. Moon A has orbital radius r, and moon
B has orbital radius 4r. Moon A takes 20 days to complete one orbit. How long does it take
moon B to complete one orbit?
TB =
rB3
(4r)3
2
´
T
=
´ 20 2 = 43 ´ 203 =160days
A
3
3
rA
r
III-Answer the following questions
[5 marks]
1. State the third ‘law of Kepler’s planetary motion’ and derive an expression for the ‘time
period’ (T) of a Planet of mass (Mp), orbiting (circular orbit) the Sun of mass (Ms) at a
distance of (r) from the center of the Sun.
The Law: “The Square of the orbital period of a planet is proportional to the cube of
the average distance from the planet to the Sun”
Please revise your notebook to derive Kepler’s third law
For a planet of mass Mp moving around the Sun, which has a mass of MS, in a circular
orbit: Because, the planet moves at a constant speed v. Newton’s second law, his law
of gravitation, and centripetal acceleration then give the following equation:
The speed v of the planet in its orbit is equal to the circumference of the orbit
divided by the time required for one revolution, T, called the period of the planet,
Substituting, the preceding expression becomes
2. Is the area swept out per unit of time by Earth moving around the Sun equal to the area
swept out per unit of time by Mars moving around the Sun? Explain.
No. The equality of the area swept out per unit of time applies to each planet
individually.
T1-SWQ
Page 4 of 4
G11-Core-Physics