Physics Chapter 4 Gravity, Projectiles, and Satellites

A projectile is launched vertically at 100 m/s. If air resistance can be neglected, at what speed does it return to its initial level?

15∘

A stone is thrown upward at an angle. Neglecting air resistance, what happens to the vertical component of its velocity along its trajectory?

At first it slows down, then reverses direction and speeds up.

Where do you weigh more—at sea level or atop one of the peaks of the Rocky Mountains? Defend your answer.

At sea level because your distance to the center of the Earth is least at sea level.

Why is it important that a satellite remain above Earth's atmosphere?

Friction with the air will exert forces on the satellite slowing it down.

If it were instead brought to half its distance from the center of the planet?

In accord with the inverse-square law, half as far means four times the force.

How would the force between a planet and its moon change if its moon were boosted to twice its distance from the center of the planet?

In accord with the inverse-square law, twice as far means one-quarter the force.

In what sense does the Moon "fall"?

It falls away from the straight path that it would follow if there were no forces acting on it.

What happens to an object close to Earth's surface if it is given a speed exceeding 11.2 km/skm/s?

It has escape velocity and moves away from the Earth never returning. It then enters an orbit about the Sun.

How does the force of gravity between two bodies change when the distance between them is tripled?

It is 1/9 of the initial force.

A stone is thrown upward at an angle. Neglecting air resistance, what happens to the horizontal component of its velocity along its trajectory?

It is constant.

A space vehicle can outrun Earth's gravity, but can it get entirely beyond Earth's gravity?

No, Earth's gravity extends to infinity, decreasing as the inverse square of the distance.

What is the status of Pluto in the family of planets?

Pluto is a dwarf planet.

How does the size of Pluto compare with that of planets in the solar system?

Pluto is much smaller.

How will the ball's speed affect the time it takes to reach the can once the ball leaves the end of the table? (Does a faster ball take a longer time to hit the floor?)

Since the ball leaves the table horizontally, its speed will not affect the time it takes to reach the floor.

Earth is farther away from the Sun in June and closest in December. In which of these two months is Earth moving faster around the Sun?

The Earth travels faster about the Sun in December than in June.

State Newton's law of universal gravitation in words. Then do the same with one equation

The force is proportional to the product of two masses and inversely proportional to the square of the distance between their center: F ~ m1m2/d^2

Why does the force of gravity change the speed of a satellite in an elliptical orbit?

The force of gravity has a component parallel to the velocity of the satellite.

What connection does Earth's curvature have with the speed needed for a projectile to orbit Earth?

The speed has to be great enough that the distance the projectile falls each second matches the Earth's curvature.

Is there change in the force of gravity between two objects when their masses are doubled and the distance between them is also doubled?

There is no change.

Why doesn't the force of gravity change the speed of a bowling ball as it rolls along a bowling lane?

There is no component of the force in the direction of motion of the ball.

Why doesn't the force of gravity change the speed of a satellite in circular orbit?

There is no component of the force in the direction of motion of the satellite.

Explain why occupants of the International Space Station are firmly in the grip of Earth's gravity, even though they have no weight.

There is no support force in free fall so they are weightless, but Earth's gravity still pulls on them and accelerates them.

Which of the following is thought to be more prevalent in the universe: ordinary matter, dark matter, or dark energy?

dark energy.

What was the cause of perturbations discovered in the orbit of planet Uranus?

gravitational pulls from Neptune.

At what part of an elliptical orbit does an Earth satellite have the greatest speed? The least speed?

greatest, when closest; least, when furthest.