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Two identical uniform spheres each of radius R are placed in contact. The gravitational force between them is F. They are then separated until the force between them is one ninth of the magnitude. What is the distance between the surfaces of the spheres?

With electostatics, it is important to remember that inthe equation giving the force between two point charges, the force is inversely proportional to the square of the distance of the charges. It is importa...
MS
Answered by Mrinank S. • Physics tutor
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What is the Schwarzschild radius of a black hole?

This is the radius of a sphere around a black hole, at the surface of which, for any object to be be free of its gravitational pull its escape velocity be equal to the speed of light.
RE
Answered by Richard E. • Physics tutor
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What is terminal velocity?

This is the maximum velocity that an object can reach when falling through a medium (like air). Note that it occurs when the drag on the object equals the pull of gravity.
RE
Answered by Richard E. • Physics tutor
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Explain what is meant by resonance.

Resonance occurs when a driving frequency is similar to the natural frequency of the system. The system is forced to vibrate at its natural frequency and therefore absorbs maximum energy, which means that th...
HK
Answered by Hafsah K. • Physics tutor
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A ball of mass 0.25 kg is travelling with a velocity of 1.2 m/s when it collides with an identical, stationary ball. After the collision, the two balls move together with the same velocity. How fast are they moving?

This question involves the principle of the conservation of momentum. Recall: Assuming no external forces act, linear momentum is always conserved . This means the total linear momentum of two objects before...
AH
Answered by Arnab H. • Physics tutor
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