Gravitation class 11.....2

Question 1

Characteristics of gravitational force

Answer 1

• it is a central force.
• it is an extremely small force.
• It is independent of the intervening medium.
• It does not depend on the presence of other bodies.
• it is valid only for spherically symmetrical point objects.
• it is a conservative force.

Question 2

the remarkable thing about acceleration due to gravity is that.

Answer 2

It is maximum on the surface and decreases whether you go up or down.

Question 3

Why in a manned satellite people experience no gravity?

Answer 3

• in a satellite around Earth every part and the parcel of the satellite has an acceleration towards the center which is exactly the value of Earth’s acceleration due to gravity at that position.
• Thus in a satellite everything inside it is in the state of freefall this is just as we are falling towards the earth from a height.

Question 4

Define weightlessness

Answer 4

When an opposite is in freefall it is weightless and this phenomenon is usually called the phenomenon of weightlessness.

Question 5

Geostationary satellites

Answer 5

• Satellites in a circular orbits around the earth in the Ecuador plane with T equal to 24 hours are called geostationary satellites.
• Clearly since the Earth rotates the same time. The satellite would appear fixed from any point on Earth.
• The INSAT group satellites sent up by India are one of such group of geostationary satellites widely used for telecommunications in India.

Question 6

Polar satellites

Answer 6

• they are low altitude (500-800 km)
• They go around the poles of the earth in the N S direction whereas the earth rotates around its axis in an east W direction.
• Since its time. 100 minutes it crosses any altitude many times a day.
• However since its height is about 500 to 800 kilometer above the earth 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 a closed distance with a good resolution.
• Information gathered by the satellites are extremely useful for remote sensing, meteorology as well as environmental studies of the Earth.

Question 7

How are radio waves reflected by ionosphere?

Answer 7

It is known that electromagnetic waves above a certain frequency are not reflected from ionosphere
radio waves used for radio broadcasts which are in the frequency range 2 MHz - 10 MHz Add below the critical frequency. They are therefore reflected by the ionosphere.
Thus radio waves broadcast from an antenna can be received at points far away where they direct wave feel 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.

Question 8

time period of moon

Answer 8

27.3 days

Question 9

Re=

Answer 9

6.4 x 10⁶ m

Question 10

geostationary or..

Answer 10

geosynchronous communication