Important Questions Class 11 Physics Chapter 8
Important Questions for CBSE Class 11 Physics Chapter 8 – Gravitation
Chapter 8 of Class 11 Physics is a very crucial chapter for the students. This chapter’s Important Question will aid in the analysis and evaluation of the students.Class 11 Physics Chapter 8 Important Questions will help you take the first step in this self-evaluation. These questions are designed to help in comprehending the types of questions that will appear on the examination. One can assess themselves and get a firm grasp of the chapter by solving these questions. This increases your confidence and helps you manage your time for the exam.
Some of the main topics discussed in Class 11 Physics Chapter 8 Gravitation are as follows.
- Kepler’s laws
- Universal law of gravitation
- The gravitation constant
- Acceleration due to:
- Gravity of the Earth
- Gravity below and above the Earth’s surface
- Gravitational potential energy
- Escape speed
- Earth satellites
- Energy of an orbiting satellite
- Geostationary and polar satellites
- Weightlessness
Extramarks offers Important Questions for Class 11 Physics Chapter 8 that cover these topics as well as other important aspects for a well-rounded preparation.
CBSE Class 11 Physics Chapter-8 Important Questions
Important Questions for Class 11 Physics Chapter 8 – Gravitation
A few of the important questions are discussed below. You can click on the link to access the complete set of questions for Chapter 8 Class 11 Physics Important Questions.
2 Marks Answers and Questions
Q1. Explain gravitation.
Ans: Any two bodies will be attracted to one another by the force of gravity, also known as gravity. There is an attraction between everything in the cosmos, however most of the time the force is too faint to be seen due to the extreme distance between the objects.
Q2. Name two factors that influence whether or not a planet has an atmosphere.
Ans: The existence of an atmosphere on a planet is determined by two factors.
- The temperature on the planet’s surface
- The presence of gravitational acceleration on the planet’s surface
Q3. At the centre of the Earth, a body is weightless. Why?
Ans: G = 0 in the centre of the Earth.
It is determined by:
w = mg
⇒w = 0
The body is therefore weightless at the centre of the Earth.
3 Marks Answers and Questions
Q1. How far from Earth’s surface does the value of g decrease to 4 of its value on Earth’s surface, given that the Earth’s radius is 6400 kilometres?
Ans: The gravity at height h is determined by
gh = gRR+h2… (1)
Given.
gh = 4 … (2)
Radius of the Earth, R = 6400 km
From (1) and (2),
4g100=gRR+h2
⇒ 4100=RR+h2
210=RR+h
⇒2R+2h = 10R
⇒2h = 8R
⇒h = 4R = 4×6400
⇒h = 25,600 km
Therefore, when the value of g is lowered to 4 of its value on the surface of the Earth, 25600 km is the height from that point.
Q2. Find expressions for an artificial satellite.
Ans: Potential energy of a satellite is
U=rF dx
Where, F is the force,
U=rGMmx2dx
Where,
M is the mass of the Earth,
m is the mass of the satellite,
x is the distance of the satellite from the Earth’s surface,
U=GMmr1x2dx
U=GMm –1xr
U=GMm –1r+1
U= –GMmr
Ans: Kinetic energy is given as
K.E. = 12mv2
Where,
m is the mass
v is the velocity
However, for artificial satellites, velocity is given as
v=GMr
Where,
G is the gravitational constant,
M is the mass of the Earth, and
r is the radius of the Earth
K.E.=12m GMr
K.E.=K=GMm2r
Ans: Total energy of a satellite is given as
TE = U+K
TE= –GMmr+GMm2r
TE= –GMm2r
Q3. Imagine if there was a planet that orbited the sun twice as quickly as the Earth. What would the size of its orbit be in relation to the Earth’s?
Ans: Time taken by the Earth to complete on revolution, Te = 1 year
Orbital radius of the Earth in its orbit, Re=1AU
Time taken by the planet to complete one revolution, Tp = 12 Te = 12 year
Orbital radius of the planet = Rp
From Kepler’s third law of planetary motion,
RpRe3= TpTe2
RpRe=TpTe23
RpRe=12123
RpRe=0.523
RpRe=0.63
As a result, the planet’s orbital radius will be 0.63 times smaller than the Earth’s.
4 Marks Answers and Questions
Q1. Assume that there are 2.5 1011 stars in our galaxy, each with a solar mass. How long will it take a star 50,000 light years from the galactic centre to make one revolution? Assume that the Milky Way is 105ly in diameter.
Ans: Mass of the Milky Way galaxy, M = 2.5 × 1011 solar mass
Solar Mass = Mass of the Sun = 2.0 × 1036 kg
Mass of our galaxy, M = 2.5 × 1011 × 2 × 1035
M = 5 × 1041 kg
Diameter of the Milky Way, d = 105 ly
Radius of the Milky Way, r = 5 × 104 ly
1 ly = 9.46 × 1015m
r = 5 × 104 × 9.46 × 1015
r = 4.73 × 1020m
Since a star rotates around the galactic centre of the Milky Way, its time period is given by
T=42r3GM12=4×3.1424.73310606.67×10-11×5×1041
T=125.27×103012
T = 1.12 × 1016s
As we know,
1 year = 365 × 24 × 60 × 60s
We get,
1s = 1365246060years
1.12 × 1016s = 1.121016365246060
∴1.121016s=3.55108years
Thus, the star will take 3.55 × 108 years to complete one revolution.
Q2. A body weighs 63N while it is on the Earth’s surface. What is the magnitude of the Earth’s gravitational pull on it at a height equal to one-half the radius of the Earth?
Ans: Weight of the body, W = 63N
Acceleration due to gravity at height h from the Earth’s surface
Re = Radius of the Earth
For h=Re2, gravity at h is given by
gh= g1+hRe2
gh= g1+122
gh= 49g
Weight of a body of mass m at height h is given as”
W’ = mgh
W’ = 49mg
W’ = 49W
W’ = 49×63
W’ = 28N
Therefore, at a height equal to half the Earth’s radius, the gravitational force exerted on the body by the Earth is 28N.
Q3. A projectile can escape from the Earth’s surface at a speed of 11.2 km/s. With three times this speed, a body is thrust out. What is the speed of a body travelling far from Earth? Ignore the sun’s and other planets’ presence.
Ans: The escape velocity of the projectile from the Earth, vesc=11.2kms-1
Projectile velocity of the projectile, vp=3vesc
Mass of the projectile = m
Projectile’s velocity far from the Earth = vf
Projectile’s total energy on the Earth = 12mvp2– 12mvesc2
The projectile’s gravitational potential energy far from the Earth is 0.
Total energy of the projectile far from the Earth = 12mvf2
From the law of energy conservation, we have
12mvp2– 12mvesc2= 12mvf2
We get,
vf=vp2–vesc2
vf=3vesc2–vesc2
vf=8vesc
vf=8×11.2
vf=31.68kms-1
Therefore, the speed of the body far from the Earth’s surface is 31.68kms-1
5 Marks Answers and Questions
Q1. One of Jupiter’s satellites, IO, has an orbital period of 1.769 days and an orbital radius of 4.22 108 metres. Prove that Jupiter’s mass is around one thousandth that of the sun.
Ans: Given,
Orbital period of IO=TIO = 1.769 days = 1.769×24×60×60s
Orbital radius IO = RIO=4.22×108m
Satellite IO is revolving around Jupiter.
Mass of Jupiter is given by
MJ = 42RIO3GTIO2 …. 1
Where,
MJ is the mass of Jupiter.
G is the Universal gravitational constant.
The orbital period of the Earth, Te = 365.25 days = 365.25 × 25 × 60 × 60s
The orbital radius of the Earth, Re = 1AU = 1.496 × 1011m
Mass of the Sun is given as
Ms=42Re3GTe2 …. 2
MSMJ=42Re3GTe2GTIO242RIO3=Re3RIO3TIO2Te2
MSMJ=1.769×24×60×60365.25×24×60×6021.496×10114.22×1083
MSMJ=1045.04
∴MSMJ~1000
We get,
MS ~ 1000 × MJ
The mass of Jupiter is therefore estimated to be approximately one thousandth that of the Sun.
Q2. A rocket is launched vertically at a speed of 5 km/s-1 from the surface of the Earth. How far does the rocket travel before coming back to Earth? Earth’s mass is 6.0 × 1024 kg; its mean radius is 6.4 × 106 m; and its gravitational constant is 6.67 × 10-11 Nm2kg-2.
Ans: Distance from the Earth’s centre = 8 × 106m
Velocity of the rocket, v = 5kms-1 = 5 × 103ms-1
Mass of the Earth, Me = 6.0 × 1024kg
Radius of the Earth, Re = 6.4 × 106m
Height reached by rocket mass m is h
At the surface of the Earth,
Total energy of the rocket = Kinetic energy + Potential energy
= 12mv2+-GMemRe
At highest point h, v = 0
Then, Potential energy = –GMemRe+h
Total energy of the rocket = 0+GMemRe+h= –GMemRe+h
From the law of conservation,
Total energy of the rocket at the Earth’s surface = Total energy of rocket at height h
Then,
12mv2+-GMemRe=-GMemRe+h
12v2=GMe1Re–1Re+h
12v2=GMeRe+h-ReRe(Re+h)
12v2=GMehReRe+hReRe
12v2=gRehRe+h
Where,
g = GMRe2=9.8ms-2 is the acceleration due to gravity on the Earth’s surface.
Clearly,
v2(Re+h) = 2gReh
v2Re = h (2gRe – v2)
h = Rev22gRe–v2
h = 6.4×25×1012100.44×106
h = 1.6 106m
Height achieved by the rocket with respect to the Earth’s centre, H is given by: H = Re + h
H = 6.4 106 + 1.6 106
We obtain,
H = 8.0 106m
The distance the rocket travels before landing on Earth is 8.0 106 metres.
Q3. A head-on collision is imminent between two stars, each of which has a solar mass of one solar mass (=2 1030 kg). Their speeds are barely perceptible at a distance of 109 kilometres. What is the rate of their collision? Each star has a 104 km radius. Assume that up until their collision, the stars won’t change. (Use the known value of G)
Ans: Mass of each star, M = 2 × 1030 kg
Radius of each star, R = 104 km = 107m
Distance between the stars, r = 109 km = 1012m
For negligible speeds, v = 0
Total energy of two stars separated at distance r is given by
TE=-GMMr+12mv2
TE= GMMr+0 ……(i)
Now, consider the case when the stars are about to collide:
Velocity of the stars = v
Distance between the centres of the stars = 2R
Total kinetic energy of both stars = 12Mv2+12Mv2=Mv2
Total potential energy of both stars = -GMM2R
Total energy of the two stars = Mv2–GMM2R …..(ii)
From the law of conservation of energy,
Mv2–GMM2R=-GMMR
v2=6.67×10-10×2×1030–11012+12×107
v2=13.34×1019–10-12+5×10-8
v2=13.34×1019×5×10-8
v2=6.67×1012
v=6.67×1012
v=2.58×106m/s
The two stars collide at a speed of 2.58 × 106 m/s.
Class 11 Physics Chapter 8 Important Questions
In order to familiarise yourself with the style, theme, depth, and techniques required to answer the questions in the exams, the set of Physics Class 11 Chapter 8 Important Questions from Extramarks is a helpful resource for exam preparation.
Importance of Class 11 Physics Chapter 8 Gravitation
Spending time studying Important Questions allows you to experiment with the best ways to respond to questions. You can improve your exam-taking skills by comparing your responses to the answers provided based on the official marking scheme. Practising these questions allows the following.
- Development of your time management skills
- Easier revision of main topics
- Focus on common exam themes
- Practise with actual exam-style questions
- Refinement of your exam answering skills
Gravitation Class 11 Important Questions
Here are some of the important questions discussed of Chapter 8 Gravitation in Class 11 Physics.
Q1. the Earth is roughly spherical. What will be the acceleration caused by gravity on Earth’s surface if its interior includes materials that is not uniformly dense on all sides?
Options:
- Aimed at the Earth’s centre, yet it varies everywhere.
- Similar in value but not pointing at the centre
- Having a constant magnitude throughout and being pointed at the centre.
- Cannot at any time be zero.
Ans: Option (d) provides the correct response: “g” cannot be zero at any time.
Q2. Three particles are positioned at positions A, B, and C, respectively, with AB = (12) and masses 2M, m, and M. (BC)
At time t = 0, they are all at rest, and a body with mass “m” is much smaller than M. What will occur at later times before any collision occurs?
Options:
- Mass “m” is moving in the direction of mass “M.”
- The mass “m” is still at rest.
- “m” goes in the direction of “2M”.
- Movements oscillate from mass “m”.
Ans: Option (c): Mass “m” goes in the direction of mass “2M”.
Class 11 Physics Chapter 8 Important Topics
- Escape Velocity
- Three laws of Kepler of planetary motion
- Universal Law of Gravitation
- Variation of the value of acceleration due to gravity ‘g’:
- With respect to depth
- With respect to the altitude
- Gravitational Potential and Gravitational Potential Energy
- Orbital Velocity
- Geo-stationary satellite
- Gravitation field intensity
- Mass and mean density of Earth
- Principle of superposition of gravitation
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- All study materials are prepared by subject matter experts.
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Conclusion
Now that you understand the advantages of solving Important Questions Class 11 Physics Chapter 8, Extramarks recommends that you attempt these questions once every few days to remember the concepts and their applications for future questions. Also, keep in mind to practise these questions first before referring to the solutions given. To pass the test with flying colours, you must work both hard and intelligently.