Case Study Questions Class 11 Physics Chapter 8 Gravitation
CBSE Class 11 Case Study Questions Physics Gravitation. Important Case Study Questions for Class 11 Board Exam Students. Here we have arranged some Important Case Base Questions for students who are searching for Paragraph Based Questions Gravitation.
At Case Study Questions there will given a Paragraph. In where some Important Questions will made on that respective Case Based Study. There will various types of marks will given 1 marks, 2 marks, 3 marks, 4 marks.
CBSE Case Study Questions Class 11 Physics Gravitation
Case Study – 1
LAW OF ORBIT: The orbit of every planet is an ellipse around the sun with sun at one of the two foci of ellipse.
LAW OF AREAS: The line that joins a planet to the sun sweeps out equal areas in equal intervals of time. Area covered by the planet while revolving around the sun will be equal in equal intervals of time. This means the rate of change of area with time is constant.
LAW OF PERIOD: According to this law the square of time period of a planet is directly proportional to the cube of the semi-major axis of its orbit.
Suppose earth is revolving around the sun then the square of the time period (time taken to complete one revolution around sun) is directly proportional to the cube of the semi major axis.
It is known as Law of Periods as it is dependent on the time period of planets. Answer the following.
1) Keplers second law is knows as
a) Law of period
b) Law of area
c) Law of gravity
d) None of these
2) Keplers third law is knows as
a) Law of period
b) Law of area
c) Law of gravity
d) None of these
3) The velocity of a planet is constant throughout its elliptical trajectory in an orbit.
a) True
b) False
c) None of these
4) State Kepler’s second law of planetary motion.
5) Two objects of masses 5kg and 10 kg separated by distance 10m. What is gravitational force between them?
Answer Key – 1
1) c
2) a
3) a
4) Keplers 3 laws are stated below.
LAW OF ORBIT: The orbit of every planet is an ellipse around the sun with sun at one of the two foci of ellipse.
LAW OF AREAS: The line that joins a planet to the sun sweeps out equal areas in equal intervals of time. Area covered by the planet while revolving around the sun will be equal in equal intervals of time. This means the rate of change of area with time is constant.
LAW OF PERIOD: According to this law the square of time period of a directly proportional to the cube of the semi-major axis of its orbit.
The force of attraction between any two unit masses separated by a unit distance is called universal gravitational constant denoted by G measured in Nm2/kg2.
5)
Case Study – 2
Satellites in a circular orbits around the earth in the equatorial plane with T = 24 hours are called Geostationary Satellites. Clearly, since the earth rotates with the same period, the satellite would appear fixed from any point on earth. It takes very powerful rockets to throw up a satellite to such large heights above the earth but this has been done in view of the several benefits of much practical application. Weight of an object is the force with which the earth attracts it. We are conscious of our own weight when we stand on a surface, since the surface exerts a force opposite to our weight to keep us at rest. The same principle holds good when we measure the weight of an object by a Spring balance hung from a fixed point e.g. the ceiling. The object would fall down unless it is subject to a force opposite to gravity. This is exactly what the spring exerts on the object. This is because the spring is pulled down a little by the gravitational pull of the object and in turn the spring exerts a force on the object vertically upwards. Now, imagine that the top end of the balance is no longer held fixed to the top ceiling of the room. Both ends of the spring as well as the object move with identical acceleration g. The spring is not stretched and does not exert any upward force on the object which is moving down with acceleration g due to gravity. The reading recorded in the spring balance is zero since the spring is not stretched at all. If the object were a human being, he or she will not feel his weight since there is no upward force on him. Thus, when an object is in free fall, it is weightless and this phenomenon is usually called the phenomenon of weightlessness. In a satellite around the earth, every part and parcel of the satellite has acceleration towards the centre of the earth which is exactly the value of earth’s acceleration due to gravity at that position. Thus in the satellite everything inside it is in a state of free fall. This is just as if we were falling towards the earth from a height. Thus, in a manned satellite, people inside experience no gravity. Gravity for us defines the vertical direction and thus for them there are no horizontal or vertical directions, all directions are the same.
1) Astronaut experiences weightlessness in space because
a) Acceleration due to gravity is zero
b) Actual weight of astronaut is zero
c) They are going with same acceleration due to gravity
d) None of these
2) Weighing machine measures
a) Mass of the person
b) Normal reaction exerted by machine on person
c) Both a and b
d) None of these
3) What is geostationary satellite?
4) What is weight? How it is measured?
5) What is weightlessness astronaut in satellite experienced by ?
Answer key – 2
1) c
2) b
3) Satellites in a circular orbits around the earth in the equatorial plane with T = 24 hours are called Geostationary Satellites. Clearly, since the earth rotates with the same period, the satellite looks like stationary object from earth.
4) Weight of an object is the force with which the earth attracts it. It is measured with the help of spring balance.
5) Weightlessness is condition in which acceleration due to gravity is balanced by satellite as it is moving and astronaut don’t feel any weight hence called weightlessness. In a satellite around the earth, every part and parcel of the satellite has acceleration towards the centre of the earth which is exactly the value of earth’s acceleration due to gravity at that position. Thus in the satellite everything inside it is in a state of free fall. Thus, in a manned satellite, people inside experience no gravity.
Case Study – 3
If a stone is thrown by hand, we see it falls back to the earth. Of course using machines we can shoot an object with much greater speeds and with greater and greater initial speed, the object scales higher and higher heights. A natural query that arises in our mind is the following: can we throw an object with such high initial speeds that it does not fall back to the earth ?
Thus minimum speed required to throw object to infinity away from earth’s gravitational field is called escape velocity.
Ve = √(2gr)
Where g is acceleration due to gravity and r is radius of earth and after solving ve 11.2 km/s. This is called the escape speed, sometimes loosely called the escape velocity. This applies equally well to an object thrown from the surface of the moon with g replaced by the acceleration due to Moon’s gravity on its surface and r replaced by the radius of the moon. Both are smaller than their values on earth and the escape speed for the moon turns out to be 2.3 km/s, about five times smaller. This is the reason that moon has no atmosphere. Gas molecules if formed on the surface of the moon having velocities larger than this will escape the gravitational pull of the moon.
Earth satellites are objects which revolve around the earth. Their motion is very similar to the motion of planets around the Sun and hence Kepler’s laws of planetary motion are equally applicable to them. In particular, their orbits around the earth are circular or elliptic. Moon is the only natural satellite of the earth with a near circular orbit with a time period of approximately 27.3 days which is also roughly equal to the rotational period of the moon about its own axis.
1.) Time period of moon is
a) 27.3 days
b) 20 days
c) 85 days
d) None of these
2. Escape velocity from earth is given by
a) 20 km/s
b.) 11.2 km/s
c.) 2 km/s
d.) None of these
3.) Define escape velocity. Give its formula
4.) Why moon don’t Have any atmosphere?
5.) What is satellite? Which law governs them?
Answer key-3
1) a
2) b
3) Minimum speed required to throw object to infinity away from earth’s gravitational field is called escape velocity.
Ve = √(2gr)
Where g is acceleration due to gravity and r is radius of earth and after solving ve 11.2 km/s. This is called the escape speed, sometimes loosely called the escape velocity.
4) The escape speed for the moon turns out to be 2.3 km/s, about five times smaller than that of earth. Therefore all atmospheric gas can go easily out of atmosphere of moon. This is the reason that moon has no atmosphere.
5) Earth satellites are objects which revolve around the earth. Their motion is very similar to the motion of planets around the Sun and hence Kepler’s laws of planetary motion are equally applicable to them.
Case Study – 4
Satellites in a circular orbits around the earth in the equatorial plane with T = 24 hours are called Geostationary Satellites. Clearly, since the earth rotates with the same period, the satellite would appear fixed from any point on earth. It takes very powerful rockets to throw up a satellite to such large heights above the earth but this has been done in view of the several benefits of many practical applications. Thus radio waves broadcast from an antenna can be received at points far away where the direct wave fails to reach on account of the curvature of the earth. Waves used in television broadcast or other forms of communication have much higher frequencies and thus cannot be received beyond the line of sight. A Geostationery satellite, appearing fixed above the broadcasting station can however receive these signals and broadcast them back to a wide area on earth. The INSAT group of satellites sent up by India is one such group of geostationary satellites widely used for telecommunications in India.
Another class of satellites is called the Polar satellites. These are low altitude (500 to 800 km) satellites, but they go around the poles of the earth in a north-south direction whereas the earth rotates around its axis in an east-west direction. Since its time period is around 100 minutes it crosses any altitude many times a day. However, since its height h above the earth is about 500-800 km, a camera fixed on it can view only small strips of the earth in one orbit. Adjacent strips are viewed in the next orbit, so that in effect the whole earth can be viewed strip by strip during the entire day. These satellites can view polar and equatorial regions. at close distances with good resolution. Information gathered from such satellites is extremely useful for remote sensing, meterology as well as for environmental studies of the earth.
1) Time period of geospatial satellite is
a) 24 hours
b) 48 hours
c) 72 hours
d) None of these
2) Polar satellites are approximately revolving at height of
a) 500 to 800km
b) 1500 to 2000 km
c) 3000 to 4000 km
d) None of these
3) Which satellite used to view polar and equatorial regions?
4) Write note on polar satellites
5) Write a note on geostationary satellite. Give its applications.
Answer Key – 4
1) a
2) a
3) Polar satellites are used to view polar and equatorial regions as they rotate on poles of earth.
4) Polar satellites are low altitude (500 to 800 km) satellites, but they go around the poles of the earth in a north-south direction. Since its time period is around 100 minutes it crosses any altitude many times a day. Information gathered from such satellites is extremely useful for remote sensing, meterology as well as for environmental studies of the earth.
5) Satellites in circular orbits around the earth in the equatorial plane with time period same as earth are called Geostationary Satellites.
Applications:- Radio waves broadcast. Satellites widely used for telecommunications in India. GPS system, navigation system , defence etc.
Case Study – 5
We know that the earth attracts every object with a certain force and this force depends on the mass (m) of the object and the acceleration due to the gravity (g). The weight of an object is the force with which it is attracted towards the earth. Mathematically
Where, W = weight of object
m = mass of object
g = acceleration due to the gravitational force
As the weight of an object is the force with which it is attracted towards the earth, the SI unit of weight is the same as that of force, that is, Newton (N). The weight is a force acting vertically downwards; it has both magnitude and direction. We have learnt that the value of g is constant at a given place. Therefore at a given place, the weight of an object is directly proportional to the mass, say m, of the object, that is, W α m. It is due to this reason that at a given place, we can use the weight of an object as a measure of its mass. Answer the following questions.
1) Dimensions of acceleration due to the gravity (g) is
a) [ML1 T-2 ]
b) [ML-1 T-2 ]
c) [ML1 T-3 ]
d) None of these
2) SI unit of weight is same as
a) Force
b) Mass
c) Acceleration due to gravity
d) None of these
3) Which of the following has same unit?
a) Mass and weight
b) Weight and force
c) Pressure and stress
d) Both b and c
4) Whether weight is scalar quantity or vector quantity? Justify your answer.
5) Differentiate between mass and weight.
Answer key-5
1) b
2) a
3) b
4) Weight is vector quantity as it has magnitude as well as direction which is always towards centre of a earth.
5) Difference between mass and weight is given below
No |
mass |
weight |
1 | Mass is amount of matter in a body. | Weight is the measure of force acting on a mass due to acceleration due to gravity. |
2 | it is a scalar quantity | it is a vector quantity |
3 | SI unit of mass is Kilogram (Kg). | SI unit of weight is Newton (N). |
4. | Mass can never be zero | Weight can be zero where gravity is zero. |
In case base study 5 ques 1 ans is wrong is answer is M-¹ L³ T-². So please correct this .