21st Century Astronomy Chapter 04

Rank the following objects in order of their circular speeds from smallest to largest.

1. An object with a mass of 15kg, orbiting Earth at the same distance as the Moon 2. An object with a mass of 5kg, orbiting Earth halfway to the Moon 3. An object with a mass of 20kg, orbiting the Earth 1/4 of the way to the moon 4. An object with a mass of 10kg, orbiting Earth just above Earth's surface According to Kepler's second law, the circular speed of an object orbiting the Earth depends only on how far away from the Earth it is located. The closer the object is to the Earth, the faster it must move in order to stay in orbit. The mass of the object itself can be ignored because it is so small compared to the Earth.

Rank the tides that occur at each date in order from strongest to weakest.

1. Full Moon in January 2. New Moon in July 3. First quarter moon in July 4. Third quarter moon in January

Compare the gravity between these pairs, each consisting of an Earth-like planet and its star. You are given the mass of the planet in Earth masses, the mass of the star in Sun masses, and the distance in AUs.

1. M(Earth) / 2M(Solar) / 2 AU 2. 4 M(Earth) / 2M (Solar) / 3 AU 3. 1 M(Earth) / 1M (Solar) / 1 AU 4. 2 M(Earth) / 1 M(Solar) / 1 AU Because the masses and distances for these pairs are stated in common units, after canceling out like terms we are left with these ratios: 1 MEarth/2 MSolar/2 AU = (1 × 2)/22 = 1/2 4 MEarth/2 MSolar/3 AU = (4 × 2)/32 = 8/9 1 MEarth/1 MSolar/1 AU = (1 × 1)/12 = 1 2 MEarth/1 MSolar/1 AU = (2 × 1)/12 = 2 This is the correct order, ranking them in increasing order of gravity.

Suppose that you drop the following objects (all of the same shape and size) off of a tall tower.Rank the objects in terms of the gravitational force on them, from smallest to largest.

1. Styrofoam apple 2. Apple 3. Gold apple

An object in a(n) __________ orbit in the Solar System will remain in its orbit forever. An object in a(n) __________ orbit will escape from the Solar System.Choose one:A. bound; unboundB. elliptical; circularC. circular; ellipticalD. unbound; bound

A. bound; unbound

If we wanted to increase the Hubble Space Telescope's altitude above Earth and keep it in a stable orbit, we also would need toChoose one:A. increase its orbital speed.B. increase its weight.C. decrease its orbital speed.D. decrease its weight.

A. increase its orbital speed.

If Earth shrank to a smaller radius but kept the same mass, the weight of each person on Earth wouldChoose one:A. increase.B. stay the same.C. decrease.

A. increase.

If an object crosses from farther to closer than the Roche limit, itChoose one:A. may be torn apart.B. slows down.C. begins to accelerate very quickly.D. can no longer be seen.

A. may be torn apart.

If the Moon were 2 times closer to Earth than it is now, the gravitational force between Earth and the Moon would beChoose one:A. 16 times stronger.B. 4 times stronger.C. 2 times stronger.D. 8 times stronger.

B. 4 times stronger.

If the Moon had twice the mass that it does, how would the strength of the lunar tides change?Choose one:A. Nothing would change.B. The highs would be higher and the lows would be lower.C. Both the highs and the lows would be higher.D. The highs would be lower, and the lows would be higher.

B. The highs would be higher and the lows would be lower.

If you went to Mars, your weight would beChoose one:A. the same as on Earth.B. lower because Mars has lower mass and a smaller radius that together produce a lower gravitational force.C. higher because you are closer to the center of the planet.D. lower because Mars has two small moons instead of one big moon, so there's less tidal force.

B. lower because Mars has lower mass and a smaller radius that together produce a lower gravitational force.

If Earth shrank to a smaller radius but kept the same mass, the gravitational force between Earth and the Moon wouldChoose one:A. increase.B. stay the same.C. decrease.

B. stay the same.

Self-gravity isChoose one:A. the force that holds objects on Earth.B. the gravitational interaction of all the parts of the body.C. the gravitational pull of a person.D. the force that holds objects like people and lamps together.

B. the gravitational interaction of all the parts of the body.

Compared to your mass on Earth, on the Moon your mass would beChoose one:A. lower because the Moon is smaller than Earth.B. lower because the Moon has less mass than Earth.C. the same; mass doesn't change.D. higher because of the combination of the Moon's mass and size.

C. the same; mass doesn't change.

Astronauts in a space shuttle can float while orbiting Earth. Why are these astronauts weightless? Choose one:A. Everything in the orbiting shuttle is shielded from Earth's gravity.B. They and the space shuttle have escaped from Earth's gravity.C. They are affected equally by the Moon's gravity and Earth's gravity.D. They are falling around Earth at the same rate as the shuttle.

D. They are falling around Earth at the same rate as the shuttle.

For a pair of objects, the center of mass is locatedChoose one:A. along the line between the two objects, closer to the less massive object.B. at the center of the less massive object.C. at the center of the more massive object.D. along the line between the two objects, closer to the more massive object.

D. along the line between the two objects, closer to the more massive object.

The connection between gravity and orbits enables astronomers to measure the __________ of stars and planets.Choose one:A. compositionsB. sizesC. distancesD. masses

D. masses

As two objects orbit one another, they are alwaysChoose one:A. on opposite sides of the center of mass, traveling in the same direction in space.B. on the same side of the center of mass, traveling in opposite directions in space.C. on the same side of the center of mass, traveling in the same direction in space.D. on opposite sides of the center of mass, traveling in opposite directions in space.

D. on opposite sides of the center of mass, traveling in opposite directions in space.

Spring tides occur only when Choose one:A. the Moon is in first or third quarter.B. the Moon, Earth, and Sun form a right angle.C. the Sun is in full phase.D. the Moon is in new or full phase.E. the Sun is near the vernal equinox in the sky.

D. the Moon is in new or full phase.

What causes the Moon to always keep the same face toward Earth?Choose one:A. tidal forces from the SunB. tidal forces from EarthC. tidal forces from the Earth and SunD. tidal locking

D. tidal locking

The "second" high tide is caused byChoose one:A. stronger gravity pulling on Earth on the side opposite the Moon.B. the Sun canceling out some of the Moon's gravity, no matter which way it pulls.C. the Sun, which always pulls in the opposite direction from the Moon.D. weaker gravity pulling on Earth on the side opposite the Moon.

D. weaker gravity pulling on Earth on the side opposite the Moon.