Conceptual Questions - Chapter 6 Gravitation 11th Science Guide Samacheer Kalvi Solutions - SaraNextGen [2024-2025]

Updated On May 15, 2024

By SaraNextGen

Conceptual Questions
Question 1.
In the following what are the quantities which that are conserved?
(a) Linear momentum of planet
(b) Angular momentum of planet
(c) Total energy of planet
(d) Potential energy of a planet
Answer:
Since there is a net force acting on the planet, its velocity changes which means its linear momentum changes. In fact, the absolute value of linear momentum changes too since the planet's speed is variable as it goes around in its elliptical orbit. So the linear

momentum of planet is not conserved. But the angular momentum about the sun is conserved. Since the torque of gravitational force is zero.

The total mechanical energy remains constant for an isolated system objects that interact with conservative forces. So, the total energy of the system of planet is conserved. The single energy of the planet is not conserved.
Question 2.
The work done by Sun on Earth in one year will be
(a) Zero
(b) None zero
(c) positive
(d) negative
Answer:
(a) Zero
Question 3.
The work done by Sun on Earth at any finite interval of time is
(a) positive, negative or zero
(b) Strictly positive
(c) Strictly negative
(d) It is always zero
Answer:
(d) It is always zero
2 \& 3. No work is done on the earth revolving around it in perfectly circular orbit. The earth revolves around the sun due to gravitational force of attraction between the sun and the earth. This force around the sun. This centripetal force is always perpendicular to the linear displacement.
Work done $=\mathrm{W}=\mathrm{F} \cdot \mathrm{d} \cos \theta$ Since $\theta=90^{\circ}$
$
\begin{aligned}
& =\mathrm{F} . \delta(0) \quad \operatorname{Cos} 90^{\circ}=0 \\
& \mathrm{~W}=0 \\
&
\end{aligned}
$

Question 4.
If a comet suddenly hits the Moon and imparts energy which is more than the total energy of the Moon, what will happen?
Answer:
A comet with small velocity and high mass, doesn't trigger the moon much. It just makes a circular shaped impact. The moon is ment for the protection for life on earth and to attain stability for the earth rotation. But a comet with large mass and with large velocity may destroy the moon completely or its impact makes the moon, go out of its orbit.
Question 5.
If the Earth's pull on the Moon suddenly disappears, what will happen to the Moon?
Answer:
Basically, the moon would become the third planet, however the orbit may change. The moon is in orbit around the earth, and what happens will depend on just when the earth disappears. The moon travels around the earth at about $1 \mathrm{~km} / \mathrm{sec}$ and the Earth - moon pair travel around the sun at about $30 \mathrm{~km} / \mathrm{sec}$. This extra $1 \mathrm{~km} / \mathrm{sec}$ movement will result in an orbit change.
Question 6.
If the Earth has no tilt, what happens to the seasons of the Earth?
Answer:
If the earth weren't tilted on its axis, there would be no seasons. And humanity would suffer.
Question 7.
A student was asked a question 'why are there summer and winter for us? He replied as 'since Earth is orbiting in an elliptical orbit, when the Earth is very faraway from .the Sun (aphelion) there will be winter, when the Earth is nearer to the Sun (perihelion) there will be winter\}. Is this answer correct? If not, what is the correct explanation for the occurrence of summer and winter?

Answer:
Early astronomers proved that Earth is spherical in shape by looking at the shape of the shadow cast by Earth on the Moon during lunar eclipse.
Question 8.
The following photographs are taken from the recent lunar eclipse which occurred on January 31,2018 . Is it possible to prove that Earth is a sphere from these photographs?
Answer:
Early astronomers proved that Earth is spherical in shape by looking at the shape of the shadow cast by Earth on the Moon during lunar eclipse.