1
PPH 0075
Physics I
Foundation in Engineering
Assignment 2
APPLIED SCIENCE DEPARTMENT
(ASD)
Centre for Foundation Studies and Extension Education
(FOSEE)
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Chapter 6
Question 1
a)
What is Newton’s law of gravity ?
[2 marks]
b)
Figure 6
shows three different masses placed at the vertices of a right angle triangle.
Calculate the total gravitational force exerted on
20 kg
mass by the other two masses.
[4 marks]
c)
i)
Prove that the total energy (
E
) of a satellite with a mass
m
moving in uniform
circular motion of orbital radius
r
can be written as
2
E
GM m
E
r
= 
where
M
E
is the mass of the earth and
G
is the universal gravitational constant.
ii)
By assuming the satellite is moving in uniform circular motion, find the
amount of work required to place a
500 kg
satellite in an orbit of
300 km
height from an orbit of
200 km
height, given the mass of the earth,
M
E
, is
5.98
x
10
24
kg
, and the radius of the earth is
R
E
=
6.38
x
10
6
m
.
[4 marks]
Question 2:
a) Suppose Malaysian’s aerospace engineer team wants to place a
1500 kg
weather satellite
into a circular orbit
350 km
above the earth surface. The earth’s radius is
R
E
=
6380 km
and its mass is
M
E
= 5.97 x 10
24
kg
.
i)
Find the speed,
v
, and time period,
T
, of the satellite.
[2 marks]
ii) How much work must be done to place this satellite in orbit?
[3 marks]
b) i) Suppose a new planet has been found (Planet
X
) by astronomer, which has a
radius
4.5
times of Earth, and a mass of
2
times of Earth. What is the acceleration,
g’
due to gravity near its surface?
[2 marks]
ii) Johannes Kepler (15721630) was a German mathematician, astronomer and
astrologer, and a key figure in 17th century astronomical revolution. Kepler made
three major discoveries that today we call Kepler’s Laws of planetary orbits. State the
THREE
laws.
[3 marks]
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 Spring '09
 none
 Mass, Johannes Kepler

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