1. A satellite revolves very near to the earth surface. Its speed should be around?
a) 5km/s
b) 8km/s
c) 2km/s
d) 11km/s
Explanation: Near the earth’s surface,
v0=√gR=7.2km/s
Approximately 8km/s.
2. The value of escape velocity on a certain planet is 2km/s. Then the value of orbital speed for a satellite orbiting close to its surface is ___________
a) 12km/s
b) 1km/s
c) √2km/s
d) 2√2km/s
Explanation: Near earth’s surface,
v0=ve/√2=2/√2=√2 km/s.
3. If gravitational constant is decreasing with time, what will remain unchanged in case of a satellite orbiting around the earth?
a) Time period
b) Orbiting radius
c) Areal velocity
d) Angular velocity
Explanation: The central gravitational force decreases which does not exert any torque. Hence the angular momentum and consequently areal velocity remain unchanged.
4. An elephant and an ant are to be projected out of the earth into space. What is the velocity needed to do so?
a) Elephant needs to be projected with a higher velocity
b) Ant should be projected with a higher velocity
c) Both should be projected with the same velocity
d) Elephant cannot be projected to space
Explanation: The escape velocity ve=√2gR, does not depend upon the mass of the projected body. Thus we need the same velocity to project an elephant and an ant into space.
5. An astronaut, while revolving in a circular orbit happens to throw a spoon outside. What will happen to the spoon?
a) It will reach the earth surface
b) It will escape the universe
c) It will remain stationary
d) It will continue to move in a circular orbit
Explanation: While revolving in a circular orbit, if a spoon is thrown outside, the spoon will continue to rotate in the same circular orbit, and chase the astronaut. It will never reach the surface of the earth.
6. It is possible to place an artificial satellite in an orbit, such that it is always visible over New Delhi.
a) True
b) False
Explanation: A satellite remains always visible only if it revolves in the equatorial plane with a period of revolution equal to that of the earth. New Delhi does not lie in the region of the equatorial plane. Hence it is not possible to place an artificial satellite in an orbit such that it is always visible from New Delhi.
7. A satellite does not need ant fuel to circle around the earth.
a) True
b) False
Explanation:The gravitational force between satellite and earth provides the centripetal force required by the satellite to move in a circular orbit.
8. A satellite orbiting the earth with speed v0. To make the satellite escape, what should be the minimum percentage increase in its velocity?
a) 41.5%
b) 44.1%
c) 41.4%
d) 40%
Explanation: Required percentage increase in velocity = (ve-v0)/v0 ×100
(√2-1)×100=41.4%.
9. A body can have energy without momentum.
a) True
b) False
Explanation: A body can have energy without momentum. There is internal energy in a body due to the thermal agitation of the particles of the body, while the vector sum if the momenta of the moving particle may be zero.
10. A particle is acted upon by a force of a constant magnitude which is always perpendicular to the velocity of the particle. The motion of the particle takes place in a plane. It follows that ___________
a) Its velocity is constant and kinetic energy is constant
b) Its acceleration and velocity is constant
c) Its kinetic energy is constant and it moves in a circular path
d) Its acceleration is constant and it moves in a circular path
Explanation: For a particle in uniform circular motion, the direction of both velocity and acceleration vectors change continuously but their magnitudes remain unchanged. The kinetic energy is not affected. Hence its kinetic energy is constant and it moves in a circular path.