Page 10 - Spotlight A+ Physics Form 4.5

Form
4 Physics Chapter 3 Gravitation

Example 10 Example 11

The Moon moves in a circular orbit around the Based on the following data about the Earth
Earth with an orbital radius of 3.83 × 10 m and orbiting around the Sun, calculate the mass of
8
6
period of orbit 2.36 × 10 s. What is the mass of the Sun.
the Earth? Radius of orbit, r = 1.50 × 10 m
11
Solution Period, T = 1 year
Mass of the Earth, Solution
4π r T = 1 year
2 3
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M =
GT 2 T = (365 × 24 × 60 × 60) s
2 3
4π r
8 3
2
4π × (3.83 × 10 ) Mass of the Sun, M =
= GT 2
(6.67 × 10 ) × (2.36 × 10 )
6 2
−11
4π × (1.50 × 10 )
11 3
2
M =
24
= 5.97 × 10 kg (6.67 × 10 ) × (365 × 24 × 60 × 60) 2
−11
= 2.01 × 10 kg
30
3.1
CHAP
3 1. State Newton’s Universal Law of Gravitation. C2
2. What are the factors that affect the magnitude of the gravitational force between two bodies? C3
3. A spacecraft of mass 150 kg is at a distance of 7.20 × 10 m from the centre of the Earth.
6
Find the gravitational force between the spacecraft and the Earth? C3
[G = 6.67 × 10 N m2 kg , mass of the Earth, M = 5.97 × 10 kg]
24
–2
–11
12
4. The planet Uranus orbits around the Sun with radius of orbit 2.87 × 10 m and period 2.64 × 10 s.
9
Calculate the mass of the Sun. C3
3.2 Kepler's Laws I, II and III
1. Kepler was a German astronomer and
mathematician who modified the heliocentric Johannes Kepler worked as an assistant to the
model of the planets moving around the Sun. astronomer Tycho Brahe. His great determination
2. Kepler succeeded in formulating three laws that drove him to study Brahe’s astronomical data for
more than ten years.
described the motion of planets around the Sun.

Activity 3.2

Aim: To sketch an elliptical shape based on the dual focus concept of an ellipse
Materials: Pencil, thread, two pieces of thumb tacks, white A4 paper, softboard and cellophane tape
Instructions:
1. The thread is tied to form a loop with a circumference of about 32 cm.
2. The two thumb tacks are stuck at points F and F on the A4 paper. The distance between F and F is
1
1
2
2
12 cm.
3. The thread loop is placed on the white paper and the pencil is held as shown in Figure 3.15.
74 3.1.6 3.2.1