Q&A Hero

Q: Why doesn't the Moon fall toward Earth like apples do? A) the great distance of the Moon prevents falling B) moon's small mass prevents falling C) moon does fall but its great distance keeps it from getting closer D) moon does fall but due to its tangential motion it also falls around Earth

Q: Compared to other fundamental forces, the Universal Gravitational Constant G indicates gravity to be a relatively A) weak force. B) strong force. C) extremely strong force.

Q: The Universal Gravitational Constant G was first measured by A) Galileo. B) Newton. C) Cavendish. D) none of these

Q: If Earth's mass somehow decreased with no change in its radius, your weight would A) decrease also. B) increase. C) remain the same.

Q: If Earth's mass somehow doubles with no change in its size, and your mass remains the same, your weight A) also doubles. B) is quadrupled. C) remains the same.

Q: If your mass doubles, your weight A) also doubles. B) is quadrupled. C) remains the same.

Q: 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

Q: 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. D) greater the force between them by the square of the distance.

Q: Newton discovered A) gravity. B) that gravity is universal. C) neither of these

Q: Why does a satellite in elliptical orbit gain speed as it moves closer to the planet? When is its kinetic energy greatest? Least? Where is its potential energy greatest? The least?

Q: What holds a circularly-moving satellite in orbit while the force of gravity pulls downward on it?

Q: Shoot a cannonball horizontally from a cannon at a mountain top 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?

Q: 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?

Q: How is stepping off a curb similar to taking a ride aboard an orbiting space vehicle?

Q: 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?

Q: If the Earth had twice its present radius and twice its present mass, what change in weight would you experience? Explain.

Q: What is the magnitude and direction of the gravitational force that acts on a person who weighs 500 N at Earth's surface?

Q: To drop a package to Earth from a satellite, project it A) straight downward. B) ahead at satellite speed. C) behind at satellite speed. D) none of the above

Q: Pioneer 10 was able to escape the solar system by A) having a sufficient escape velocity at launch. B) "bouncing off" Jupiter like a tennis ball bouncing off an approaching tennis racket. C) refueling via solar cells. D) nuclear-powered sustained thrust.

Q: A vertically oriented rocket that is able to sustain a continuous upward velocity of 8 km/s will A) eventually escape from Earth. B) be unable to escape Earth. C) maintain a fixed orbit around Earth.

Q: A projectile that is fired vertically at 8 km/s from Earth's surface will A) go into circular orbit about Earth. B) rise and fall back to Earth's surface. C) follow an uncertain path. D) escape from Earth.

Q: A projectile that is fired vertically at 5 km/s from the Earth's surface will A) go into a circular orbit about Earth. B) go into an elliptical orbit about Earth. C) rise and fall back to Earth's surface. D) none of the above

Q: Consider a monkey wrench released at rest at the far edge of the solar system that 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.

Q: 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.

Q: Escape speed for a rocket is less from A) Earth. B) the Moon. C) the Sun. D) same for each

Q: Escape speed for a rocket is greatest from A) Earth. B) the Moon. C) the Sun. D) same for each

Q: Escape speed from Earth is A) 8 km/s. B) 9.8 km/s. C) 11.2 km/s. D) 42.2 km/s.

Q: 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.

Q: Acceleration is greater for a satellite in elliptical orbit when it is A) closest to Earth. B) farthest from Earth. C) the same at both locations

Q: Gravitational force is greater for a satellite in elliptical orbit when it is at the A) apogee (farthest point). B) perigee (closest point). C) zenith. D) same acceleration at all of the above places.

Q: The parabolic path of a cannonball fired from a mountain top is actually A) a segment of a circle if firing is horizontally. B) a segment of an ellipse. C) a path for escape speed. D) none of the above

Q: An Earth satellite in an elliptical orbit travels slowest when it is A) nearest the Earth. B) farthest from the Earth. C) neither of these

Q: An Earth satellite in an elliptical orbit travels fastest when it is A) nearest the Earth. B) farthest from the Earth. C) neither of these

Q: A satellite in an elliptical orbit travels at constant A) velocity. B) speed. C) acceleration. D) all the above E) none of the above

Q: From Earth, one satellite appears to overtake another. The faster satellite that is seen to overtake the other is A) higher. B) lower. C) can't say

Q: 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 of these D) none of the above

Q: 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

Q: 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.

Q: A lunar month is about 28 days. If the Moon were closer to Earth than it is now, the lunar month would be A) more than 28 days. B) unchanged at 28 days. C) less than 28 days.

Q: 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.

Q: 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 of these D) none of the above

Q: Minimal orbit speed about Earth is about 8 km/s. Minimal orbital speed for a satellite about Jupiter would be A) less than 8 km/s. B) greater than 8 km/s. C) about 8 km/s.

Q: Minimal orbit speed about Earth is about 8 km/s. Minimal orbital speed for a satellite about the Moon would be A) less than 8 km/s. B) greater than 8 km/s. C) about 8 km/s.

Q: The speeds of the planets about the Sun depend on A) their distances from the Sun. B) the masses of the planets. C) both of these D) none of the above

Q: The fastest moving planet in a solar system is the A) smallest planet. B) most massive planet. C) planet nearest the Sun. D) planet farthest from the Sun. E) none of the above

Q: Compared with the period of satellites in orbit close to Earth, the period of satellites in orbit far from Earth is A) greater. B) less. C) the same. D) not enough information

Q: A satellite near Earth makes a full circle in about 90 minutes. Much farther from Earth, say at the distance to the Moon, time for a full circle would be A) 90 minutes. B) less than 90 minutes. C) about 28 days. D) not enough information E) none of the above

Q: 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

Q: The circular path of a satellite orbiting Earth is characterized by a constant A) speed. B) acceleration. C) radial distance. D) all the above E) none of the above

Q: 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 of these D) none of the above

Q: 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

Q: For each 8-km segment of a satellite in close Earth orbit, the "drop" toward Earth is about A) 5 m. B) 10 m. C) also 8 km.

Q: The force of gravity on a satellite in circular orbit doesn't change its speed because the force is A) small compared to other forces on it. B) canceled by centrifugal force. C) perpendicular to its direction of motion. D) very weak due to altitude.

Q: The force of gravity on a bowling ball rolling along a horizontal surface doesn't change its speed because the force is A) small compared to the ball's weight. B) canceled by the normal force. C) perpendicular to its direction of motion. D) canceled by friction.

Q: What holds Earth satellites up so they don't crash into Earth? A) gravity B) centripetal force C) centrifugal force D) the absence of air resistance E) nothing, they continually fall fast enough around Earth not to crash

Q: Without air resistance, a projectile fired horizontally at 8 km/s from a mountain top 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

Q: The Moon does not crash into Earth because A) Earth's gravitational field is weak at the Moon's distance. 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

Q: For the astronauts inside an orbiting space vehicle the force of gravity that acts on them is A) zero. B) mainly due to Earth below. C) mainly due to the mass of the space vehicle. D) mainly due to nearby planets and stars. E) none of the above

Q: The Moon continually falls toward Earth, but doesn't get closer because A) the distance of fall is very small. B) its tangential velocity causes it to fall around as well as toward Earth. C) gravitation is extremely weak at the Earth-Moon distance.

Q: 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.

Q: The radial velocity of an Earth satellite is its velocity A) parallel to the surface of Earth. B) perpendicular to the surface of Earth. C) attributed to satellites moving in any direction. D) none of the above

Q: The tangential velocity of an Earth satellite is its velocity A) parallel to the surface of Earth. B) perpendicular to the surface of Earth. C) attributed to satellites moving in any direction.

Q: An Earth satellite is simply a projectile A) freely falling around Earth. B) floating motionless in space near Earth. C) approaching Earth from outer space.

Q: Ignoring air resistance, what maximum speed 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 from the bottom of the net? A) 12.0 m/s B) 16.0 m/s C) 24.0 m/s D) 48.0 m/s

Q: 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) about 1 s. C) more than 1 s.

Q: Two motorcycle stunt drivers, one light and the other much heavier, ride their motorcycles up and off an inclined ramp at identical speeds. They both rise in the air and land downrange. Neglecting air resistance, the one to attain the greatest height and greatest range is the A) light driver. B) heavy driver. C) both the same

Q: An airplane flies at 40 m/s at an altitude of 50 m. The pilot drops a heavy package that falls to the ground below. Neglecting air resistance, the package will 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

Q: An airplane flying overhead drops a care package directly over Mike at rest in his Corvette. Neglecting air resistance, the package will land A) behind Mike. B) upon Mike and his Corvette. C) well ahead of Mike and his Corvette.

Q: A softball player determines her pitching speed by throwing a ball horizontally from an elevation of 20 m above the ground. The ball lands 50 m downrange. What is her pitching speed? A) 5 m/s B) 10 m/s C) 20 m/s D) 25 m/s E) none of the above

Q: A softball player determines her pitching speed by throwing a ball horizontally from an elevation of 5 m above the ground. The ball lands 20 m downrange. What is her pitching speed? A) 5 m/s B) 10 m/s C) 20 m/s D) 25 m/s E) none of the above

Q: Air resistance on a high-speed projectile shortens its A) range. B) maximum height. C) both of these D) none of the above

Q: After a stone that is thrown straight up reaches the top of its path and then falls downward, its acceleration is A) greater than at the top of its path. B) less than at the top of its path. C) the same as at the top of its path.

Q: If there were no gravity, a cannonball fired upward at 45 would follow a straight-line path. Due to gravity, however, at the end of 3 s it is A) 5 m below the straight line. B) 10 m below the straight line. C) 15 m below the straight line. D) 20 m below the straight line. E) more than 20 m below the straight line.

Q: If there were no gravity, a ball thrown upward at an angle would follow a straight-line path. Due to gravity, however, at the end of 2 s it is A) 5 m below the straight line. B) 10 m below the straight line. C) 15 m below the straight line. D) 20 m below the straight line. E) more than 20 m below the straight line.

Q: If there were no gravity, a ball thrown upward at an angle would follow a straight-line path. Due to gravity, however, 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. D) 20 m below the straight line. E) more than 20 m below the straight line.

Q: 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

Q: 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) is only the force due to gravity, always directed downward. D) none of the above

Q: 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

Q: With no air resistance, a projectile fired at 50 has the same range as if it were fired at A) 40. B) 45. C) 55. D) 60.

Q: Which of the following has the largest momentum relative to Earth? A) a tightrope walker crossing Niagara Falls B) a pickup truck speeding along a highway C) a Mack truck parked in a lot D) a dog running down the street