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Universal Gravitation
Kepler's
U
Misc.
100

Calculate the force of gravity between a 72kg artist sitting 0.2m away from his 3kg easel.

3.6*10-7 N

100

Which statement correctly describes planetary orbits according to Kepler’s First Law?

A. Planets move in circular orbits centered on the Sun
B. Planets move in ellipses with the Sun at one focus
C. Planets move in ellipses with the Sun at the center
D. Planets move in spiral paths toward the Sun

B. Planets move in ellipses with the Sun at one focus

100

True or False: Increasing a satellite’s orbital radius increases its kinetic energy.

False-- KE decreases with radius

100

If a rocket is launched from Earth’s surface with a speed equal to half the escape speed...

(A) It escapes
(B) It reaches infinity with zero speed
(C) It rises and falls back to Earth
(D) It enters circular orbit

(C) It rises and falls back to Earth

200

A planet has the same mass as Earth but twice the radius. What is the gravitational acceleration at its surface in terms of gearth?

gearth / 4

200

Mars' period is about 687 days. Determine the mean distance of Mars from the Sun using Earth as a reference. The Earth is 1.5*1011m from the sun.

r=2.3*1011m

(365/687)2=(1.5*1011/r)3

200

A 1000-kg satellite moves from a circular orbit at radius Rearth to a radius 2Rearth. Find the change in gravitational potential energy.


(GMm)/(2R)

200

A satellite orbits Earth in a circular orbit at an altitude equal to Earth’s radius. Find the orbital speed in terms of 'g' and Rearth

v=sqrt((gR)/2)

300

An object of mass m1 is a distance r away from a mass of m2. There is a gravitational force of F between them. If m1 is tripled and the distance between the two objects is increased from r to 3r, what is the new gravitational force?

F/3

300

A planet moves in an elliptical orbit around a star. At point P the planet is closer to the star than at point Q. Which statement is correct?

A. The planet’s speed is the same at P and Q
B. The planet moves faster at Q
C. The planet moves faster at P
D. The planet’s acceleration is zero at P

C. The planet moves faster at P

300

A 500kg satellite is in a circular orbit of radius 7*106m around Earth. It is boosted into a new circular orbit of radius 1.4*107m. How much work must the engines do?

7.13*109 J

300

A satellite orbits Earth just above the surface. Find the orbital speed.

7900 m/s