For a spherical planet to act like a "point mass", so that externally F=GmM/r2, it

A) must have constant density throughout.
B) must have a mass << r c2 / (2G).
C) must have spherical mass symmetry.
D) can not be hollow inside.


C

Physics & Space Science

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Projectile Motion: A rock is thrown from the upper edge of a tall cliff at some angle above the horizontal. It reaches its highest point and starts falling down. Which of the following statements about the rock's motion are true just before it hits the ground? (There could be more than one correct choice.)

A. Its horizontal velocity component is zero. B. Its velocity is vertical. C. Its vertical velocity component is the same as it was just as it was launched. D. Its horizontal velocity component is the same as it was just as it was launched. E. Its speed is the same as it was just as it was launched.

Physics & Space Science

Radiative energy is

A) heat energy. B) energy from nuclear power plants. C) energy carried by light. D) energy used to power home radiators. E) energy of motion.

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What is a quasar?

A) a starlike object that actually represents a bright patch of gas in the Milky Way B) a very large galaxy thought to be formed by the merger of several smaller galaxies, typically found in the center of a galaxy cluster C) a specialized astronomical instrument for observing distant stars D) the extremely bright center of a distant galaxy, thought to be powered by a supermassive black hole E) another name for very bright stars of spectral type O

Physics & Space Science

If y = 0.02 sin (30x? 400t) (SI units), the velocity of the wave is

A. 3/40 m/s. B. 40/3 m/s. C. 60?/400 m/s. D. 400/60? m/s. E. 400 m/s.

Physics & Space Science