# Gravitation - Short Question Solution | Physics Grade XI

### Gravitation Short Question Solution

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# Gravitation - Short Question Answers

1. A person sitting in a satellite of the earth feels weightlessness, but a person standing on the moon has weight though the moon is satellite of the earth. Why?
An astronaut inside a small spaceship orbiting around the earth does not experience any gravity. But an astronaut on the moon which is also orbiting around the earth does experience gravity because of force of gravity of spaceship is negligible compared to that of moon.

2. If earth suddenly stops rotating about its axis, what would be the effect on ‘g’?
We know that, acceleration due to gravity on the earth surface, R radius of earth and ω is the angular velocity of rotation of the earth. The value of g` decreases due to rotation of earth. If earth stops rotating (ω = 0), it is clear from the equation (i) that g` = g. Thus, value of g` increases to g. This effect is maximum at equator and minimum at poles because at pole the value of g is not changed.

3. What is a black hole? Explain its characteristic nature.
Black hole is that stage of star when it has completely burnt its nuclear fuel. Its characteristics natures are:
1. Its specific gravity is high, that no light can escape from its surface.
2. Its surface is black since no light can escape from its surface.
3. Its escape velocity is more than the speed of light.
4. An astronaut in a space capsule orbiting the earth experiences weightlessness. Why?
The centripetal force necessary to keep the space-ship in an orbit around the earth is provided by the gravitational force between the earth and the spaceship. Hence, the only force of gravity that an astronaut in an orbiting space-ship experiences is that which is due to the gravitational force exerted by the spaceship. But the space-ship is small and its force is also negligibly small that the astronaut doesn’t experience any gravity.

5. What do you mean by geo-stationary satellite?
A satellite put in a circular orbit concentric and coplanar with the equatorial plane of the earth and at a height, such that its period of revolution is just 24 hours is called geostationary satellite. The geo-stationary satellite moves around the earth at distance about 36,000km from the surface of the earth.

6. Why moon has no atmosphere?
Due to the low value of acceleration due to gravity, the escape velocity on the moon is quite small about 2km/ s. the root mean square velocity of different gases is greater than the escape velocity on the moon. As a result, all the gases molecules escaped out from moon with the passage of time. Hence, the moon has no atmosphere.

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