chp 10 - homework questions
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 does a projectile drop in 1 second? What is the speed needed for a projectile to orbit Earth?
5 m, 8 km/s
What exactly is a projectile?
An object that continues in motion by its own inertia
Why is it important that the projectile in the preceding question be 100 km or higher above Earth?
To avoid air resistance
What is the ratio of escape speed from Earth to circular orbital speed? Ignore air resistance.
1.41
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
How much time does it take for a complete revolution of a satellite in close orbit about Earth?
90 minutes
Is the sum of kinetic and potential energies a constant for satellites in circular orbits, in elliptical orbits, or in both?
Both
Who gathered the data that showed planets traveling in elliptical paths around the Sun? Who discovered elliptical orbits? Who explained them?
Brahe, Kepler, Newton
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.
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.
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
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.
Do your answers to the preceding question depend on the angle at which the projectile is launched?
No
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.
Why doesn't the force of gravity change the speed of a bowling ball as it rolls along a bowling lane?
The force is at a right angle to the motion.
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.
Why is kinetic energy a constant for a satellite in a circular orbit but not for a satellite in an elliptical orbit?
The force of gravity is perpendicular to the motion in a circular orbit but not in an elliptical orbit.
What was the direction of the force on a planet in a circular orbit in Kepler's thinking? In Newton's thinking?
The force was parallel to the motion for Kepler, whereas the force was toward the planet for Newton.
For orbits of greater altitude, is the period longer or shorter? Is the speed faster or slower?
The period is longer and the speed is slower.
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"?
a) The projectile falls 5 m for every 8 km and so does Earth. b) A projectile can "fall around Earth" if the distance it falls matches the curvature of Earth. c) In a circular orbit around a spherical planet, the force and the fall are always toward the center. >>>>All of the above.
