physics exam pt. 4
Escape speed from Earth is any speed equal to or greater than __________.
11.2 km/s
Why does the vertical component of velocity for a projectile change with time, whereas the horizontal component of velocity doesn't change?
Gravity is a purely vertical force.
According to Kepler, the paths of planets about the Sun are
ellipses.
The horizontal and vertical components of velocity for a projectile are __________.
independent of each other
A satellite coasting at constant speed in a circular orbit
is nevertheless accelerating.
When the potential energy of a satellite decreases
its kinetic energy correspondingly increases.
Which of these vary for satellites in circular orbits?
kinetic energy. momentum. speed. (none of the above)
An Earth satellite in an elliptical orbit travels fastest when it is
nearest Earth.
A projectile that is fired vertically from the surface of Earth at 5 km/s will
rise and fall back to Earth's surface.
A projectile that is fired vertically from the surface of Earth at 8 km/s will
rise and fall back to Earth's surface.
Acceleration due to gravity on the Moon is less than on Earth, and the Moon is smaller than Earth. This means that compared to an Earth satellite, a satellite in close orbit about the Moon would travel
slower.
Which of these vary for satellites in elliptical orbits?
speed. kinetic energy. momentum. all of the above
The circular path of a satellite orbiting Earth is characterized by a constant
speed. radial distance. acceleration. (all of the above)
An Earth satellite in an elliptical orbit has its smallest speed
when farthest from Earth
A projectile is launched at 30° above ground level. What other angle at the same speed will result in the same range?
60°
How much time does it take for a complete revolution of a satellite in close orbit about Earth?
90 minutes
When Dr. Hewitt releases the two projectiles, which one hits the ground first?
Both balls hit the ground at the same time.
Why do the two objects hit the table at the relative times that they do?
Gravity pulls the same amount on both, and they both drop the same distance.
Why does the force of gravity change the speed of a satellite in an elliptical orbit?
Gravity slows the satellite as it moves away and speeds it up on its return.
A stone is thrown upward at an angle. What happens to the magnitude of the vertical component of its velocity as it rises? As it falls?
It decreases while rising, but it increases while falling.
Predict how the vertical component of the velocity will change with time after the projectile is fired.
It first decreases to zero and then increases in the opposite direction.
Predict how the horizontal component of the velocity will change with time after the projectile is fired.
It stays constant.
A stone is thrown upward at an angle. What happens to the horizontal component of its velocity as it rises? As it falls?
Rising or falling, it does not change.
For an Earth satellite in an elliptical orbit, list all the values that do change.
Speed, gravitational force, and distance from Earth
Which ball (if either) has the greatest speed at the moment of impact?
The ball thrown horizontally
Why doesn't the force of gravity change the speed of a satellite in circular orbit?
The force is at a right angle to the velocity.
Which projectile spends more time in the air, the one fired from 30∘ or the one fired from 60∘?
The one fired from 60∘
Why is it important that the projectile in the preceding question be 100 km or higher above Earth?
To avoid air resistance
When Dr. Hewitt releases the two objects, how can we tell whether one of the objects hits the ground first or whether they both hit at the same time?
We are able to hear the two balls fall.
How far does a projectile drop in 1 second? What is the speed needed for a projectile to orbit Earth?
5 m, 8 km/s
At what part of an elliptical orbit does an Earth satellite have the greatest speed? The lowest speed?
Greatest nearest Earth; lowest furthest from Earth
The Moon does not crash into Earth because
Moon has a sufficient tangential speed.
What did Kepler discover about the periods of planets and their distances from the Sun?
The period squared was proportional to the distance cubed.
How can a projectile "fall around the Earth"?
In a circular orbit around a spherical planet, the force and the fall are always toward the center. The projectile falls 5 m for every 8 km and so does Earth. A projectile can "fall around Earth" if the distance it falls matches the curvature of Earth. (All of the above)
For an Earth satellite in circular orbit, list all the values that do not change.
Only speed, gravitational force, and distance from Earth
Is the sum of kinetic and potential energies a constant for satellites in circular orbits, in elliptical orbits, or in both?
circular and elliptical
The kinetic energy of a satellite remains constant when the satellite follows a __________.
circular path
Kepler was the first to be credited for discovering that planets follow __________.
elliptical paths
A projectile is launched vertically at 100 m/s. If air resistance can be ignored, at what speed will it return to its initial level?
100 m/s
A projectile is launched upward at an angle of 70° from the horizontal and strikes the ground a certain distance downrange. For what other angle of launch at the same speed would this projectile land just as far away?
20°
A projectile falls beneath the straight-line path it would follow if there were no gravity. How many meters does it fall below this line if it has been traveling for 1 s? For 2 s?
5 m, 20 m
How far below a straight-line path does a horizontally projected projectile fall in the first second of fall?
5 meters
Who gathered the data that showed planets traveling in elliptical paths around the Sun? Who discovered elliptical orbits? Who explained them?
Brahe, Kepler, Newton
According to Kepler, the speed of a planet is slowest when it is
farthest from the Sun
