Preview Extract
Chapter 4 Gravity, Projectiles, and Satellites
4.1 The Universal Law of Gravity
1) Newton discovered
A) gravity.
B) that gravity is universal.
C) neither
Answer: B
2) According to Newton, the greater the masses of interacting objects, the
A) less the gravitational force between them.
B) greater the gravitational force between them.
C) greater the force between them by the square of the masses.
Answer: B
3) What is the force of gravity on a 500-N woman standing on Earth's surface?
A) 50 N
B) 250 N
C) 500 N
D) 598 N
E) 5000 N
Answer: C
4) If the mass of Earth somehow increased with no change in radius, your weight would
A) increase also.
B) decrease.
C) remain the same.
Answer: A
5) If your mass remained the same while the mass of Earth doubled while staying the same size,
your weight would
A) be the same.
B) double.
C) quadruple.
D) be eight times as much as now.
E) none of the above
Answer: B
6) Consider two planets in space that gravitationally attract each other. If the mass of one planet
is doubled, and the distance between them doesn't change, then the force between them is
A) one-quarter.
B) half as much.
C) twice as much.
D) four times as much.
E) none of the above
Answer: C
7) Consider two planets in space that gravitationally attract each other. If the masses of both
planets are doubled, and the distance between them doesn't change, then the force between them
is
A) one-quarter.
B) half as much.
C) twice as much.
D) four times as much.
E) none of the above
Answer: D
8) The Earth and the Moon gravitationally attract each other. Does the more massive Earth
attract the Moon with a greater force, the same force, or less force than the Moon attracts the
Earth? What reasoning guides your answer?
Answer: The force between each is the same, in accord with Newton's third law. Note also from
Newton's formula for gravitation that the force does not depend on the order of the masses, but
depends simply on the product.
9) What is the magnitude and direction of the gravitational force that acts on a person who
weighs 500 N at the Earth's surface?
Answer: 500 N straight downward, which is the weight of the person.
10) If the Earth had twice its present radius and twice its present mass, what would happen to
your weight? Explain.
Answer: If only the radius of the Earth were twice, you'd have one-quarter your weight. If only
the mass of the Earth were twice, you'd have twice your weight. Taken together, your weight
would be half.
11) How is stepping off a curb similar to taking a ride aboard the space shuttle?
Answer: In both instances you experience weightlessness. The main difference is the time
involved. Stepping off a curb involves apparent weightlessness for a very brief time. Orbiting in
the space shuttle involves all the time you're coasting in orbit.
4.2 Gravity and Distance: The Inverse-Square Law
1) According to Newton, the greater the distance between gravitationally interacting objects, the
A) less the gravitational force between them.
B) more the gravitational force between them.
C) constancy of the force between them.
Answer: A
2) According to Newton, the closer gravitationally interacting objects are to each other, the
A) less the gravitational force between them.
B) more the gravitational force between them.
C) constancy of the force between them.
Answer: B
3) Two objects move toward each other due to gravity. As the objects get closer and closer, the
force between them
A) increases.
B) decreases.
C) remains constant.
Answer: A
4) Two objects move toward each other due to gravity. As the objects get closer and closer, the
acceleration of each
A) increases.
B) decreases.
C) remains constant.
Answer: A
5) If Earth's mass decreased to one-half its original mass with no change in radius, your weight
would
A) decrease to one-quarter.
B) decrease to one-half.
C) remain the same.
D) none of the above
Answer: B
6) If Earth's mass doubled with no change in radius, your weight would
A) increase by one-quarter.
B) double.
C) be four times as much.
D) none of the above
Answer: A
7) If your mass remains unchanged while both the mass of Earth and its radius doubles, your
weight
A) remains the same.
B) doubles.
C) quadruples.
D) increases by eight times.
E) reduces by half.
Answer: E
8) If the masses of two planets doubles and the distance between them also doubles, the force
between them would be
A) one-quarter.
B) half as much.
C) twice as much.
D) four times as much.
E) none of the above
Answer: E
9) If the masses of two planets doubles and the distance between reduces by half, the force
between them would be
A) unchanged.
B) half as much.
C) twice as much.
D) four times as much.
E) none of the above
Answer: A
10) If the radius of the Earth somehow decreased with no change in mass, your weight would
A) increase.
B) not change.
C) decrease.
Answer: A
11) If the radius of the Earth somehow increased with no change in mass, your weight would
A) increase.
B) not change.
C) decrease.
Answer: A
12) If the Sun were twice as massive,
A) its pull on the Earth would double.
B) Earth's pull on the Sun would double.
C) both
D) neither
Answer: C
13) A woman who normally weighs 400 N stands on top of a very tall ladder so she is one Earthradius above Earth's surface. What is her weigh there?
A) zero
B) 100 N
C) 200 N
D) 400 N
E) none of the above
Answer: B
14) A very massive object A and a less massive object B move toward each other under the
influence of gravity. Which force, if either, is greater?
A) the force on A
B) the force on B
C) both forces are the same
Answer: C
15) An object is placed exactly halfway between the Earth and the Moon. The object will fall
toward the
A) Earth.
B) Moon.
C) neither
Answer: A
16) At some point between Earth and the Moon, the forces due to gravity on a space traveler
would be the same. This point is
A) nearer Earth.
B) nearer the Moon.
C) mid-way between Earth and the Moon.
D) none of the above
Answer: B
17) The amount of gravitational force that acts on a space vehicle that orbits Earth is
A) nearly zero.
B) nearly as much as the vehicle's weight on Earth's surface.
C) the same as the vehicle's weight on the Earth's surface.
Answer: B
18) The force of gravity acts on all apples on an apple tree. Some apples are twice as far from the
ground. Such twice-as-high apples of the same mass, have
A) 1/4 the weight.
B) 1/2 the weight.
C) practically the same weight.
Answer: C
19) When the distance between two stars decreases by half, the force between them
A) decreases by one-quarter.
B) decreases by one-half.
C) increases to twice as much.
D) increases to four times as much.
E) stays the same.
Answer: D
20) When the distance between two stars doubles, the force between them
A) decreases by one-quarter.
B) decreases by one-half.
C) increases to twice as much.
D) increases to four times as much.
E) remains the same.
Answer: A
21) In the vacuum of outer space, there is no
A) gravity.
B) atmospheric pressure.
C) both
Answer: B
22) The planet Jupiter is about 300 times as massive as Earth, yet on its surface you would weigh
only about 3 times as much. This is because
A) your mass is 100 times less on Jupiter.
B) Jupiter is significantly farther from the Sun.
C) Jupiter's radius is 10 times Earth's radius.
D) you are 100 times more weightless there.
E) none of the above
Answer: C
23) A supplier wants to make a profit by buying gold by weight at one altitude and selling it at
the same price per kilogram at another altitude. The supplier should
A) buy at a high altitude and sell at a low altitude.
B) buy at a low altitude and sell at a high altitude.
C) disregard altitude because it makes no difference.
Answer: A
24) Each of us weighs a tiny bit less inside the ground floor of a skyscraper than we do on the
ground away from the skyscraper because the
A) gravitational force is shielded inside the building.
B) mass of the building attracts us upward slightly.
C) both
D) none of the above
Answer: B
25) How far must one travel to completely be beyond Earth's gravity?
A) to a region above the Earth's atmosphere
B) to a region well beyond the Moon
C) to a region beyond the solar system
D) forget it; you can't travel far enough
Answer: D
4.3 Weight and Weightlessness
1) Inside a freely falling elevator you would experience no
A) gravitational force.
B) weight.
C) both
D) none of the above
Answer: B
2) Inside a freely falling elevator your
A) acceleration is zero.
B) weight is zero.
C) gravitational interaction with Earth is zero.
D) all the above
E) none of the above
Answer: B
3) Passengers in a high-flying jumbo jet feel their normal weight in flight. Passengers in an
orbiting space vehicle do not because passengers are
A) beyond the main pull of Earth's gravity.
B) above the Earth's atmosphere.
C) without support forces.
D) all the above
E) none of the above
Answer: C
4) Weight can be simulated in a space vehicle if the vehicle is
A) falling.
B) in a circular orbit about Earth.
C) rotating.
D) none of the above
Answer: C
5) Strictly speaking, when you step off a curb you are momentarily
A) in orbit.
B) weightless.
C) in space.
Answer: B
4.4 Universal Gravitation
1) The Sun is spherical due to
A) Earth circling it.
B) Earth and Moon circling it.
C) gravitation.
D) none of the above
Answer: C
2) Perturbations of planets are due to
A) interplanetary forces.
B) deviations from straight-line paths.
C) uneven masses of planets.
D) none of the above
Answer: A
3) The planet Neptune was discovered by perturbations of
A) Uranus.
B) its moons.
C) Pluto.
D) none of the above
Answer: A
4) Dwarf planet Pluto was discovered by perturbations of
A) Jupiter.
B) Saturn.
C) Uranus and Neptune.
D) all of the above
Answer: C
5) Chapter 4 in your textbook cites a link between Newton's Universal Law of Gravity and
A) biological processes.
B) chemical processes.
C) geological processes.
D) the U.S. Constitution.
E) none of the above
Answer: D
4.5 Projectile Motion
1) Roll a bowling ball off the edge of a table. As it falls, its horizontal component of motion
A) decreases.
B) remains constant.
C) increases.
Answer: B
2) A rock is thrown upward at 50° with respect to the horizontal. As it rises, its vertical
component of velocity
A) increases.
B) remains unchanged.
C) decreases.
Answer: C
3) A rock is thrown upward at 50° with respect to the horizontal. As it rises, its horizontal
component of velocity
A) increases.
B) remains unchanged.
C) decreases.
Answer: B
4) A bullet fired from a rifle begins to fall
A) as soon as it leaves the barrel.
B) after air friction reduces its speed.
C) neither
Answer: A
5) A projectile is fired horizontally. With no air resistance it maintains its horizontal component
of velocity because
A) no forces act on it.
B) no horizontal forces act on it.
C) of no initial vertical component of velocity.
D) all of the above
E) none of the above
Answer: B
6) A projectile is launched straight upward at 50 m/s. If air resistance is negligible, its speed
upon returning to its starting point is
A) less than 50 m/s.
B) 50 m/s.
C) more than 50 m/s.
Answer: B
7) A ball is thrown upwards and caught when it returns. Neglecting air resistance, the speed with
which it is caught is
A) more than its initial speed.
B) less than its initial speed.
C) the same as its initial speed.
Answer: C
8) Neglecting air resistance, after a ball leaves your hand when you toss it upward, the force on it
A) gradually decreases until the ball reaches the top of its path.
B) first acts upward and then downward after reaching the top.
C) s only the force due to gravity, always directed downward.
D) none of the above
Answer: A
9) If a projectile is fired straight up at a speed of 10 m/s, neglecting air resistance, the time it
takes to reach the top of its path is
A) 1 s.
B) 2 s.
C) 10 s.
D) not enough information
Answer: A
10) If a projectile is fired straight up at a speed of 10 m/s, neglecting air resistance, the total time
to return to its starting position is
A) 1 s.
B) 2 s.
C) 10 s.
D) 20 s.
E) not enough information
Answer: B
11) A stone is thrown horizontally from the top of a cliff. One second after leaving your hand it
drops a vertical distance of
A) 5 m.
B) 10 m.
C) 15 m.
Answer: A
12) An object is thrown vertically into the air. Because of air resistance, the time for its descent
will be
A) longer than the ascent time.
B) shorter than the ascent time.
C) equal to the ascent time.
D) not enough information
Answer: A
13) Throw an object at an angle upward. With no gravity it will follow a straight-line path. But
because of gravity, at the end of 1 s, it is
A) 5 m below the straight line.
B) 10 m below the straight line.
C) 15 m below the straight line.
Answer: A
14) A hunter fires a bullet from a horizontally-held rifle while simultaneously dropping another
bullet from the side of the rifle. Which bullet hits the ground first?
A) the dropped one
B) the fired one
C) both hit at the same time
Answer: C
15) A hunter aims a rifle at an angle of 10° above the horizontal. The hunter fires a bullet while
simultaneously dropping another bullet from the side of the rifle. Which bullet hits the ground
first?
A) the dropped one
B) the fired one
C) both hit at the same time
Answer: A
16) A hunter aims a rifle at an angle of 10° below the horizontal. The hunter fires a bullet while
simultaneously dropping another bullet from the side of the rifle. Which bullet hits the ground
first?
A) the dropped one
B) the fired one
C) both hit at the same time
Answer: B
17) A bullet fired horizontally hits the ground in 0.5 s. If it had been fired with twice the velocity
it would have hit the ground in
A) less than 0.5 s.
B) more than 0.5 s.
C) 0.5 s.
Answer: C
18) A gun with a muzzle velocity of 100 m/s is fired horizontally from a tower. Neglecting air
resistance, how far downrange will the bullet be 1 s later?
A) 50 m
B) 98 m
C) 100 m
D) 500 m
E) none of the above
Answer: C
19) A projectile is launched at an angle of 15° above the horizontal and lands downrange. With
no air resistance, what other projection angle for the same speed would produce the same
downrange distance?
A) 30°
B) 45°
C) 50°
D) 75°
E) 90°
Answer: D
20) A projectile is thrown into the air at an angle of 50° and lands on a target that is at the same
level the projectile started. With no air resistance it will also land on the target if it is thrown at
an angle of
A) 40°.
B) 45°.
C) 55°.
D) 60°.
E) none of the above
Answer: A
21) Two projectiles are fired at equal speeds but different angles. One is fired at an angle of 30 °
and the other at 60°. With no air resistance, the projectile to hit the ground first will be the one
fired at
A) 30°.
B) 60°.
C) both hit at the same time
Answer: A
22) After a rock that is thrown straight up reaches the top of its path and is starting to fall back
down, its acceleration is
A) greater than when it was a the top of its path.
B) less than when it was at the top of its path.
C) the same as it was at the top of its path.
Answer: C
23) A ball player wishes to determine pitching speed by throwing a ball horizontally from an
elevation of 5 m above the ground. The player sees the ball land 20 m down range. What is the
player's pitching speed?
A) 5 m/s
B) 10 m/s
C) 20 m/s
D) 25 m/s
E) none of the above
Answer: C
24) An airplane flies at 40 m/s at an altitude of 50 m. The pilot drops a heavy package, which
falls and strikes the ground. Neglecting air resistance, where does the package land?
A) beneath the plane
B) 400 m behind the plane
C) 500 m behind the plane
D) more than 500 m behind the plane
E) none of the above
Answer: A
25) Two motorcycle stunt drivers, one light and the other much heavier, drive their motorcycles
up and off an inclined ramp at identical speeds. They both rise in the air and land downrange.
Neglecting air drag, the one to attain the greatest height and greatest range is the
A) light driver.
B) heavy driver.
C) both the same
Answer: C
26) A ball is thrown horizontally from the top of a tall cliff. Three seconds later, the ball has
fallen a vertical distance of
A) 20 m.
B) 30 m.
C) 45 m.
D) depends on the initial horizontal speed of the ball
Answer: C
27) The hang time of an athlete who moves horizontally 2.0 m during a 1.25-m-high jump is
A) less than 1 s.
B) 1 s.
C) more than 1 s.
Answer: B
28) Ignoring air drag, what is the maximum speed that can be given to a horizontally moving
tennis ball as it clears the net 1.25 m high to remain within the edge of the court, which is 12.0 m
distant?
A) 12.0 m/s
B) 16.0 m/s
C) 24.0 m/s
D) 48.0 m/s
Answer: C
29) An Earth satellite is simply a projectile freely falling around the Earth.
A) true
B) false
C) sometimes true and sometimes false
Answer: A
30) Toss a rock at an angle into the air and it follows a curved path. Its velocity at any instant can
be resolved into horizontal and vertical components. Which of these components changes with
time, and why?
Answer: Only the vertical component changes with time because it is in the same direction as
Earth's gravity. Going upward, the rock is going against gravity and its upward component of
velocity decreases. Going downward, the vertical component increases as gravity increases the
speed of the rock. But the horizontal component is neither with nor against gravity. No force acts
sidewise (barring air resistance), which is why there is no change in the horizontal component of
velocity.
31) Shoot a cannonball horizontally from a cannon at the top of a mountain and it gains speed as
it falls and hits the ground below. But fire the cannonball fast enough for circular orbit and no
change in speed occurs. Why?
Answer: The cannonball that hits the ground has a component of force in its direction of motion.
This increases the speed of the falling cannonball. But when it is fired in circular orbit, the force
acts perpendicular all along the path-with no component of force in the direction of motion. Put
another way, in circular orbit the force of gravity does no work on the cannonball. Therefore
there is no change in speed. But if fired at a lower speed, where the cannonball arcs downward, a
component of force in the direction of motion exists. Then work is done and the cannonball gains
kinetic energy.
4.6 Fast-Moving Projectiles–Satellites
1) Tangential velocity is velocity
A) parallel to the surface of the Earth.
B) perpendicular to the surface of the Earth.
C) attributed to satellites moving in any direction.
Answer: A
2) Planets would crash into the Sun if it weren't for
A) their tangential velocities.
B) their vast distances from the Sun.
C) the inverse-square law.
D) their relatively small masses.
E) the fact that they are beyond the main gravitation of the Sun.
Answer: A
3) For the astronauts inside an orbiting space vehicle, there is no force of Earth's gravity acting
on them. This statement is
A) always true while in orbit.
B) sometimes true while in orbit.
C) always false.
Answer: C
4) The reason the Moon does not crash into Earth is that
A) Earth's gravitational field is weak at the Moon.
B) the gravitational pull of other planets keeps the Moon up.
C) the Moon has a sufficient tangential speed.
D) the Moon has less mass than Earth.
E) none of the above
Answer: C
5) A projectile is fired vertically from the surface of the Earth at 8 km/s and remains in a vertical
path. The projectile will
A) go into circular motion about Earth.
B) rise and fall back to Earth's surface.
C) follow an uncertain path.
Answer: B
6) Without air resistance, a projectile fired horizontally at 8 km/s from a mountaintop will
A) accelerate downward at g as it moves horizontally.
B) trace a curve that matches Earth's curvature.
C) return to its starting position and repeat its falling behavior.
D) all the above.
E) none of the above.
Answer: D
7) What prevents satellites such as the space shuttle from falling?
A) gravity
B) centripetal force
C) centrifugal force
D) the absence of air resistance
E) nothing, they continually fall around and around Earth
Answer: E
8) A "weightless" astronaut in an orbiting space vehicle is
A) shielded from Earth's gravitational effects.
B) beyond the pull of gravity.
C) without a support force.
D) all of the above
E) none of the above
Answer: C
9) Earth satellites are typically more than 100-km high so as to mainly be above the Earth's
A) atmosphere.
B) gravitational influence.
C) both
Answer: A
4.7 Circular Satellite Orbits
1) The circular orbit of a satellite orbiting the Earth is characterized by a constant
A) speed.
B) acceleration.
C) radial distance.
D) all the above
E) none of the above
Answer: D
2) The period of a satellite, the time it takes for a complete revolution, depends on the satellite's
A) mass.
B) weight.
C) radial distance.
D) all the above
E) none of the above
Answer: C
3) A satellite near Earth makes a full circle in about 90 minutes. How long would a satellite
located as far away as the Moon take to orbit Earth?
A) 90 minutes
B) less than 90 minutes
C) about 28 days
D) not enough information
E) none of the above
Answer: C
4) Compared with the period of satellites in orbit close to Earth, the period of satellites in orbit
far from Earth is
A) longer.
B) shorter.
C) the same.
D) not enough information
Answer: A
5) The fastest moving planet in a solar system is
A) the smallest planet.
B) the most massive planet.
C) the planet nearest the Sun.
D) the planet farthest from the Sun.
E) any planet, for they all move at the same speed.
Answer: C
6) The speeds of the planets about the Sun depend on
A) their distances from the Sun.
B) the masses of the planets.
C) both
D) neither
Answer: A
7) Minimal orbit speed about Earth is about 8 km/s. Minimal orbital speed about the Moon
would be
A) less than 8 km/s.
B) more than 8 km/s.
C) about 8 km/s.
Answer: A
8) Minimal orbit speed about Earth is about 8 km/s. Minimal orbital speed about Jupiter would
be
A) less than 8 km/s.
B) more than 8 km/s.
C) about 8 km/s.
Answer: B
9) The planet Jupiter takes a longer time to travel around the Sun than Earth because Jupiter
A) has farther to go.
B) goes slower.
C) both
D) none of the above
Answer: C
10) A lunar month is about 28 days. If the Moon were farther from Earth than it is now, the lunar
month would be
A) more than 28 days.
B) less than 28 days.
C) about 28 days.
Answer: A
11) A lunar month is about 28 days. If the Moon were closer to Earth than it is now, the lunar
month would be
A) less than 28 days.
B) more than 28 days.
C) unchanged at 28 days.
Answer: A
12) The Earlybird communication satellite hovers over the same point on Earth's equator
indefinitely because
A) forces other than Earth's gravity act on it.
B) it pulls as hard on Earth as Earth pulls on it.
C) it is beyond the main pull of Earth gravity.
D) it is kept aloft by ground control.
E) its orbital period is 24 hours.
Answer: E
13) Communications and weather satellites always appear at the same place in the sky because
these satellites are
A) beyond the pull of Earth's gravitational field.
B) moving at a speed just short of escape velocity.
C) orbiting Earth with a 24-hour period.
D) stationary in space.
E) none of the above
Answer: C
14) The International Space Station orbits at an average 360-km altitude so that it is mainly
above Earth's
A) atmosphere.
B) gravitation.
C) both
Answer: A
15) From Earth, one satellite appears to overtake another. The faster satellite is
A) higher.
B) lower.
C) can't say
Answer: B
16) Why do satellites remain in orbit while the force of gravity pulls downward on them?
Answer: They remain in orbit because the force of gravity pulls perpendicular to the motion of
the satellite. With no component of force in the direction of motion, no change in speed occursonly a change in direction.
4.8 Elliptical Orbits
1) A satellite in an elliptical orbit travels at constant
A) velocity.
B) speed.
C) acceleration.
D) all the above
E) none of the above
Answer: E
2) An Earth satellite is in an elliptical orbit. The satellite travels fastest when it is
A) nearest the Earth.
B) farthest from the Earth.
C) neither
Answer: A
3) An Earth satellite is in an elliptical orbit. The satellite travels slowest when it is
A) nearest the Earth.
B) farthest from the Earth.
C) neither
Answer: B
4) Compared to the speed a satellite loses when traveling from nearest to farthest points from
Earth, the speed gained when returning from farthest to nearest is
A) less.
B) the same.
C) more.
Answer: B
5) The force of gravity does work on a satellite when it is in
A) circular orbit.
B) elliptical orbit.
C) both
D) neither
Answer: B
6) Acceleration is greatest for a satellite in elliptical orbit when it is
A) closest to Earth.
B) farthest from Earth.
C) same at both places
Answer: A
7) Why does a satellite in elliptical orbit gain speed as it moves closer to the planet? When is its
kinetic energy the greatest? The least? Where is its potential energy greatest? The least?
Answer: The sum of a satellite's potential and kinetic energies remains constant if the satellite is
in a closed orbit about a planet. As the satellite moves closer to the planet, it falls with gravity
and gains speed. Potential energy decreases, kinetic energy correspondingly increases, and hence
speed increases. As it moves farther from the planet, it moves against gravity, its kinetic energy
decreases, and its potential energy increases. Its potential energy is greatest when the satellite is
farthest from the planet, and least when it is closest to the planet.
4.9 Escape Speed
1) Escape speed from Earth is
A) 8 km/s.
B) 9.8 km/s.
C) 11.2 km/s.
D) 42.2 km/s.
Answer: C
2) Escape speed for a rocket is greatest from
A) Earth.
B) the Moon.
C) the Sun.
D) same for each
Answer: C
3) Escape speed for a rocket is less from
A) Earth.
B) the Moon.
C) the Sun.
D) same for each
Answer: B
4) Traveling from Earth to the Moon requires that a rocket have
A) less than escape speed from Earth.
B) more than escape speed from Earth.
C) any sustained speed if time isn't a factor.
Answer: C
5) Consider a monkey wrench released at rest at the far edge of the solar system. Suppose that it
drops to Earth by virtue of only Earth's gravity. The wrench will strike Earth's surface with a
speed of about
A) 10 m/s.
B) 8 km/s.
C) 11 km/s.
D) the speed of light.
Answer: C
Test Bank for Conceptual Physical Science
Paul Hewitt, John Suchocki, Leslie Hewitt
9780321752932, 9780134060491
