Physics chapter 10

A communications satellite with a 24 hour period hovers over a fixed point on Earth and to Earth observers, seems motionless. Why is it placed only in an orbit in the plane of Earth's equator? In your discussion, think of the satellite's orbit as a ring around Earth.

Communication satellites only appear motionless because their orbital period coincides with the daily rotation of the Earth.

If you stopped an Earth satellite dead in its tracks, in would simply crash into Earth. Why, then, don't the communications satellites that "hover motionless" above the same spot on Earth crash into Earth?

Communication satellites only appear motionless because their orbital period coincides with the daily rotation of the earth.

Upon which does the speed of a circling satellite not depend: the mass of the satellite, the mass of Earth, the distance of the satellite from Earth?

Doesn't depend on the mass of the satellite.

You read in an article about astronauts in a major magazine that about 62 miles up the atmosphere ends and gravity becomes very weak? What error is made here?

Gravity doesn't become much weaker when the atmosphere ends.

Discuss why Hawaii is the most efficient launching site in the US for nonpolar satellites. In your discussion include a look at the spinning Earth from above either pole and compare it to a rotating turntable.

Hawaii is closer to the equator, and therefore has a greater tangential speed about the polar axis. This speed could be added to the launch speed of a satellite and thereby save fuel.

In 2000-2001, NASA's Near Earth Asteroid Rendervous spacecraft orbited around the 20 mile long asteroid Eros. Do you speculate that the orbital speed of this spacecraft is greater or less than 8 km.s. Discuss and defnd your answers.

If the asteriod is 20 miles long, its orbital tie would need to be faster than 8km/s because that is equivalent to 5mi/s and it seems impossible for anything to travel 5 miles in one second

How could an astronaut in a space shuttle "drop" an object vertically to Earth?

It could be dropped by firing its straight backward at the same speed of the satellite. Then its speed realtive to Earth would be zero, and it would fall straight downward.

If you have ever watched the launching of an Earth satellite, you may have noticed that the rocket starts vertically upward, then departs from a vertical course and continues its climb at an angle. WHy does it start vertically? Why doesn't it continue vertically.

It starts out vertically so it gets through the part of the atmosphere that will slow it down. It doesn't continue vertically because it needs to be horzontal in order to have enough tangenital speed to orbi.

Would the speed of a satellite in close circular orbit about Jupiter be greater than, equal to, or less than 8 km/s.

Looking at escape speed it is evident that Jupiter's escape speed is much larger than that of Earth's so the speed of the satellite in close circular orbit about jupiter would be greater than 8km/s

If you toss a ball vertically upward in a uniformly moving train, it returns to its starting place. Will it do the same if the train is accelerating. Explain.

No, because while in the air the train changes its motion. It will land behind you.

Suppose you drop a care package from an airplane traveling at constant velocity, and further suppose that air resistance doesn't affect the falling package. What will be its falling path as observed by someone at rest on the ground, not directly below but off to the side where there's a clear view? What will be the falling path as observed by you looking downward from the airplane?

Observed from someone at rest, it will fall in a parabolic path. Observed from one looking downward, it will fall directly below them.

What happens to an Earth satelitte's period when the satellite is placed into a higher orbit?

Period is greater for satellites farthest from Earth.

When a rifle is being fired at a distant target, why isn't the barrel aligned so that it points exactly at the target?

The bullet will encounter a parabolic fall, so if you aim slightly higher than the target, the bullet will land at the target.

Since the moon is gravitationally attracted to Earth, why doesn't it simply crash into Earth?

The moon's tangential velocity is what keeps the Moon coasting around the Earth rather than crashing into it. If its tangenital velocity were reduced to zero, then it would fall straight into the Earth!

In an accidental explosion, a satellite breaks in half while circular orbit about Earth. One half is brought momentariily to rest. What is the fate of the half brought to rest? Discuss what happens to the other half.

The other half will continue to orbit and the half that is brought momentarity to rest has a tangential speed of zero and it falls toward Earth. It will more than likely burn up as it enters the atmosphere.

A rocket coasts in an elliptical orbit around Earth. To attain the greatest amount of KE for escape for a given amount of fuel, should it fire its engines to acclerate forward when it is at the apogee or at the perigee. Let the formal Fd=change KE. be your guide to thinking. Suppose the thrust F is brief and of the same duration in iether case. Then consider the distance d the rocket would travel during this brief burst at the apogee and at the perigee.

The perigee because that is the point closest to the Earth, thus having the most KE.

Suppose you roll a ball off a tabletop. Will this time to hit the floor depend on the speed of the ball?

The time to hit the floor is independent of the ball's speed. The ball is rolling along the horizontal axis which means it will only bring the ball to the end of the table faster. I will hit the floor at the same speed because it will have the same force due to gravity in the vertical direction.

In the absence of air resistance, why doesn't the horizontal component of a projectile's motion change, while the vertical component does?

There are no forces horizontally so there is no horizontal acceleration, hence the horizontal component of velocity doesn't change. Gravitation acts vertically, which is why the vertical component of velocity changes.

When a satellite in circular orbit slows, perhaps due to the firing of a retro docket, it ends up gaining more speed than it had initially. Why?

Upon slowing, it spirals in toward the earth and in doing so has a component of gravitational force in its direction of motion which causes it to gain speed

Why does a satellite burn up when it descends in to the atmosphere? And why doesn't it burn up when it ascends through the atmosphere?

When it ascends through the atomsphere it can control how fast it gets through by using fuel to get there. When it descends, it can't control how fast its falling, and thi scauses a lot of rcition and the KE is transferred into heat energy and when there is too much heat energy it will cause it to burn up.

Why is work done by the force of gravity on a satellite when it moves from one part of an elliptical orbit to another, but no work is involved when it moves from one part of circular orbit to another?

When there is an elliptical orbit there is a component of force in the same direction, so no work is done.

When a satellite coasts in a circular orbit at constant speed about Earth, is it accelerating? If so, in what direction? If not, why not?

Yes, it is accelerating. It accelerates due to the gravitational force between it and the Earth. The acceleration is toward the Earth's center.

Ignoring air resistance, could a satellite be put into orbit in a circular tunnel beneath Earth's surface? Discuss.

Yes. A satellte can orbit any distance from Earth's center of mass. Its orbiting speed would be less because things orbit faster when closer to the surface of the Earth

A friend claims that bullets fired by some high-powered rifles travel for many meters in a straight-line path before they start to fall. Another friend disputes this claim and states that all bullets from any rifle drop beneath a straight-line path a vertical distance given by 1/2gt^2 and that the curved path is apparent for low velocities and less apparent for high velocities. Now it's your turn: discuss whether or not all fired bullets drop the same vertical distance in equal times.

Yes. All objects in free fall, near the Earth's surface accelerate down at 10 m/s/s when we disregard air friction.

A park ranger shoots a monkey hanging form a branch of a tree with a tranquilizing dart. The ranger aims direclty at the monkey, not realizing that the dart will follow a parabolic path and thus will fall below the monkey. The monkey, however, sees the dart leave the gun and lets go of the branch to avoid being hit. Will the monkey be hit anyway?

\Yes because the ranger shot towards the monkey in a direct path, the dart will drop lower than he intended, and the monkey will fall downward as well because he let go of the brach. They will both meet below the intended path.

The positions of a satellite in elliptical orbit are indicated. Rank these quantities from greatest to least: a)gravitational force. b)speed. c)Momentum d)KE e)PE f)Total energy (KE + PE) g)Acceleration

a. A, B, C, D b. A, B, C, D c. A, B, C, D d. A, B, C, D e. D, C, B, A f. A=B=C=D g. A, B, C, D

A ball is tossed off the edge of a cliff with the same speed but at different angles, as shown. From greatest to least the a)initial PEs of the balls relative to the ground below. b)initial KEs of the ball when tossed. c)KEs of the balls when they hit the ground below. d)times of flight while airborn.

a. A=B=C b. A=B=C c. A=B=C d. B, A, C

When you jump upward, your hang time is the time your feet are off the ground. Does hang time depend on your vertical component of velocity when you jump, your horizontal component of velocity or both ? Defend your answer.

hang time is when you jump upward, so the vertical component of velocity is what you depend on. The horizontal component had nothing to do with hang time.

As part of their training before going into orbit, astronauts experience weightlessness when riding in an airplane that is flown along the same parabolic trajectory as a freely falling projectile. A classmate says that gravitational forces on everything inside the plane during this maneuver cancel to zero. Another classmate looks to you for confirmation. What is your response?

it may seem to cancel, but it doesn't. They are experiencing a state of free fall, so there is no support force, so that's why they are feeling weightlessness.

A satellite in a circular orbit about the Moon fires a small probe in a direction opposite to the velocity of the satellite is the same as the satellite's speed realtive to the moon, describe the motion of the probe. If the probe's relative speed is twice the speed of the satellite, why would it pose a danger to the satellite>

it will drop vertically toward the moon. If fired at twice the speed it and the satellite would have the same speed in opposite directions, and they could collid after half an orbit

If a satellite circled Earth at a distance equal to the Earth-Moon distance, how long would it take for it to make a complete orbit? In other words, what would be its period.

it would be the same time that it takes the moon to complete an orbit. The period would be 27.3 days

At what point in its elliptical orbit about the Sun is the acceleration of Earth toward the Sun a maxiumu? At what point is it a minimum? Defend your answers.

maximum where gravitational force is maximum, when earth is closest to the sun, at the perigee. At the apogee, force and accelerate are minimum.

Which requires less fuel: launching a rocket to escape speed from the Moon or from Earth? Defend your answer.

the moon because it has only one sixth of the gravitational pull that Earth does