NCERT Physics Class 11 Exemplar Ch 8 Gravitation Part 5

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MCQ Type Questions

Q. 30 Show the nature of the following graph for a satellite orbiting the earth.

(a) KE vs orbital radius R

(b) PE vs orbital radius R

(c) TE vs orbital radius R.

Answer:

PE and KE of satelite

PE and KE of Satelite

PE and KE of satelite

Q.31 Shown are several curves (Fig.). Explain with reason, which ones amongst them can be possible trajectories traced by a projectile (neglect air friction).

Trajectory due to gravitation

Trajectory Due to Gravitation

Trajectory due to gravitation

Answer: The trajectory of a particle under gravitational force of the earth will be a conic section (for motion outside the earth) with the centre of the earth as a focus. Only (c) meets this requirement.

Q.32 An object of mass m is raised from the surface of the earth to a height equal to the radius of the earth, that is, taken from a distance R to 2R from the centre of the earth. What is the gain in its potential energy?

Answer:

Q.33 A mass m is placed at P a distance h along the normal through the centre O of a thin circular ring of mass M and radius r (Fig).

Gravitation force

Gravitation Force

Gravitation force

If the mass is removed further away such that OP becomes 2h, by what factor the force of gravitation will decrease, if h = r?

Answer: Only the horizontal component (i.e. along the line joining m and O) will survive. The horizontal component of the force on any point on the ring changes by a factor:

Large Answer

Q. 34 A star like the sun has several bodies moving around it at different distances. Consider that all of them are moving in circular orbits. Let r be the distance of the body from the centre of the star and let its linear velocity be v, angular velocity ω, kinetic energy K, gravitational potential energy U, total energy E and angular momentum l. As the radius r of the orbit increases, determine which of the above quantities increase and which ones decrease.

Answer: As r increases:

decreases.

decreases.

K decreases because v increases.

E increases because

L increases because

Q.35 Six-point masses of mass m each are at the vertices of a regular hexagon of side l. Calculate the force on any of the masses.

Answer: AB=C

Force along AD due to m at F and B

Force along AD due to masses at E and C

Force due to mass M at D

Forces in hexagon

Forces in Hexagon

Forces in hexagon

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