Exam 2 Review
How much work is done on a satellite in a circular orbit about Earth?
0
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.
When the speed of a moving car is doubled, how much more kinetic energy does it have?
It has four times as much.
power
power=work/time interval
Which of the following quantities represent mass? Check all that apply. 12.0 lbs 0.34 g 120 kg 1600 kN 0.34 m 411 cm 899 MN
0.34 g 120 kg
What is the ratio of escape speed from Earth to circular orbital speed? Ignore air resistance.
1.41 11.2/9.8
Escape speed from Earth is any speed equal to or greater than __________.
11.2 km/s
Which of the following quantities would be acceptable representations of weight? Check all that apply. 12.0 lbs 0.34 g 120 kg 1600 kN 0.34 m 411 cm 899 MN
12.0 lbs 1600 kN 899 MN
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
Which requires more work: lifting a 50-kg sack a vertical distance of 2 m or lifting a 25-kg sack a vertical distance of 4 m?
Both take the same 1000 J.
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.
Why is centrifugal force in a rotating frame called a "fictitious force"?
It is not a fundamental force of nature. Instead, it is a force that only appears in an accelerating frame of reference
How does the thickness of paint sprayed on a surface change when the sprayer is held twice as far away?
It is ¼ as thick.
Compared with a car moving at some original speed, how much work must the brakes of a car supply to stop a car that is moving twice as fast? How will the stopping distances compare?
It takes four times the work and four times the stopping distance.
A car is raised a certain distance in a service-station lift, thus giving it potential energy relative to the floor. If it were raised twice as high, how much more potential energy would it have?
It would have twice as much potential energy.
Kepler's second law
Kepler's second law tells us that as an object moves around its orbit, it sweeps out equal areas in equal times. Because all the areas shown here are equal, the time it takes the comet to travel each segment must also be the same. Kepler's second law tells us that the comet sweeps out equal areas in equal times. Because the area triangle is shorter and squatter for the segments nearer to the Sun, the distance must be greater for these segments in order for all the areas to be the same. the fact that that the comet sweeps out equal areas in equal times implies that its orbital speed is faster when it is nearer to the Sun and slower when it is farther away.
If both sacks in the preceding question are lifted their respective distances in the same time, how does the power required for each compare? How about for the case in which the lighter sack is moved the same distance in half the time?
Lifted in the same time, the power is the same. The light sack moving in half the time requires double the power
For an Earth satellite in circular orbit, list all the values that do not change.
Only speed, gravitational force, and distance from Earth
How does speed affect the friction between a road and a skidding tire?
Speed has no effect on the friction.
An apple hanging from a limb has potential energy because of its height. If it falls, what becomes of this energy just before it hits the ground? When it hits the ground?
The energy is kinetic energy before it hits the ground; it is thermal energy after.
What happens to the force of attraction between two planets when the distance between them is doubled?
The force decreases to one quarter.
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 centers: F ~ m1m2/d^2.
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 happens to the force of attraction between two planets when the masses of both are doubled?
The force quadruples.
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.
A tapered cup rolled on a flat surface makes a circular path. What does this tell you about the tangential speed of the rim of the wide end of the cup compared with that of the rim of the narrow end?
The tangential speed of the wide end is faster.
What is the Newtonian synthesis?
The union of terrestrial laws and cosmic laws
If you are not wearing a seat belt in a car that rounds a curve, and you slide across your seat and slam against a car door, what kind of force is responsible for your slide: centripetal, centrifugal, or no force?
There is no force as viewed by someone outside the car. To them you move in a straight line.
Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that was moving upward at constant velocity? Downward at constant velocity?
There would be no more compression and no more expansion for both upward and downward motion.
What is the source of energy in sunshine?
Thermonuclear fusion energy
When you whirl a can at the end of a string in a circular path, what is the direction of the force you exert on the can?
Toward the center of the circle
A force sets an object in motion. When the force is multiplied by the time of its application, we call the quantity impulse, and an impulse changes the momentum of that object. What do we call the quantity force multiplied by distance?
Work
Where do you weigh more: at the bottom of Death Valley or atop one of the peaks of the Sierra Nevada? Why?
You weigh more in Death Valley because you are closer to the center of Earth.
Give an example of when your weight is greater than mg. Give an example of when your weight is zero.
Your weight is greater than mg when you are accelerating upward. Your weight is zero when you are in free fall
Inelastic collision
a collision in which the colliding objects become distorted and or generate heat during the collision and possibly stick together
Elastic collision
a collission in which the colliding objects rebound with no lasting deformation or heat generation
The skater's potential energy is Now observe the potential energy bar on the Bar Graph. As the skater is skating back and forth, where does the skater have the most potential energy? the same everywhere. at its maximum value at the lowest point of the track. at its maximum value at the locations where the skater turns and goes back in the opposite direction.
at its maximum value at the locations where the skater turns and goes back in the opposite direction. Notice that the skater's potential energy is greatest where the kinetic energy is the lowest, and vice versa.
Is the sum of kinetic and potential energies a constant for satellites in circular orbits, in elliptical orbits, or in both?
both
When traveling twice as fast your kinetic energy is increased _______.
by four. KE=1/2mv^2
The tangential speed on the outer edge of a rotating carousel is _______.
greater than toward the center tangential speed is linear speed along a curved path
The horizontal and vertical components of velocity for a projectile are __________.
independent of each other
momentum
inertia in motion p=mv; momentum=mass*velocity
What are the units of measurement for tangential speed? For rotational speed?
m/s for tangential, RPM for rotational
The constant G in Newton's equation ______
makes the units of measurement consistent
An object is lifted from the surface of a spherical planet to an altitude equal to the radius of the planet. As a result, which of the following changes in the properties of the object take place?
mass remains the same; weight decreases
The foci of the elliptical path for an Earth satellite are __________.
one at Earth's center and the other elsewhere
energy
that which can change the condition of matter.
impulse
the product of force and the time interval during which the force acts impuse=Ft = change in momentum
About how far below a straight-line path does a satellite in close Earth orbit fall in the first second of fall?
5 meters
How far below a straight-line path does a horizontally projected projectile fall in the first second of fall?
5 meters
The crew of a cargo plane wishes to drop a crate of supplies on a target below. To hit the target, when should the crew drop the crate? Ignore air resistance.
Before the plane is directly over the target
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
Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that was accelerating upward? Downward?
More compressed while accelerating upward, but less compressed while accelerating downward
If the string that holds a whirling can in its circular path breaks, what kind of force causes it to move in a straight- line path: centripetal, centrifugal, or no force? What law of physics supports your answer?
No force; Newton's first law (inertia) whats in motion tends to stay in motion
For an Earth satellite in an elliptical orbit, list all the values that do change.
Speed, gravitational force, and distance from Earth
On a rotating turntable, how do tangential speed and rotational speed vary with distance from the center?
Tangential speed increases with distance. Rotational speed is constant.
Two cars are raised to the same elevation on service-station lifts. If one car is twice as massive as the other, compare their gains of potential energy.
The car with twice the mass has twice the potential energy.
How does the force of gravity between two bodies change when the distance between them is doubled?
The force decreases to ¼ of its initial value.
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.
Is it an inward force or an outward force that is exerted on the clothes during the spin cycle of an automatic washing machine? What about the direction of the force on the water?
The force is inward on clothes and there is none on water.
How can a projectile "fall around the Earth"?
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. In a circular orbit around a spherical planet, the force and the fall are always toward the center.
How does the tapered rim of a wheel on a railroad train allow one part of the rim to have a greater tangential speed than another part when it is rolling on a track?
The tangential speed is proportional to the radius. The inside of the wheel rolls on a larger radius than the outside of the wheel.
When is the potential energy of something significant?
When the potential energy changes
Why doesn't the force of gravity change the speed of a satellite in circular orbit?
Why doesn't the force of gravity change the speed of a satellite in circular orbit?
When G was first measured by Henry Cavendish, newspapers of the time hailed his experiment as the "weighing Earth experiment." Why?
With a known mass, a scale, and the radius of Earth, you can calculate the unknown mass of Earth if you know G.
Where on the track is the skater's kinetic energy the greatest?
at its maximum value at the lowest point of the track. The kinetic energy of an object is given by K=(1/2)mv2, where v is the speed of the object and m is the mass of the object. Thus, the skater's kinetic energy is greatest at the lowest point of the track, where the skater is moving the fastest.
The kinetic energy of a satellite remains constant when the satellite follows a __________.
circular path
mechanical energy
energy due to the position or the movement of something; PE or KE or PE+KE
When you lift twice the load twice as high, in half the time, the increase in potential energy is _______.
four times. PE=mgh (mass* height)
work
w=fd
The gravitational field on the surface of the earth is stronger than that on the surface of the moon. If a rock is transported from the moon to the earth, which properties of the rock change?
weight only
