# Physics Chapter 10*

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According to Kepler’s laws, the paths of planets about the sun are

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ellipses.

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Both Newton and Kepler considered forces on the planets. Kepler hypothesized the direction of the forces was

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along their directions of travel.

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Which of the following is not a vector quantity?

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speed

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An airplane that flies at 100 km/h in a 100 km/h hurricane crosswind has a ground speed of

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141 km/h.

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An airplane travels at 141 km/h toward the northeast. What is its component of velocity due north?

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100 km/h

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A rock is thrown upward at 50 degrees with respect to the horizontal. As it rises, neglecting air drag, its vertical component of velocity

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decreases.

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A rock is thrown upward at 50 degrees with respect to the horizontal. As it rises, neglecting air drag, its horizontal component of velocity

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remains unchanged.

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A stone is thrown horizontally from the top of a cliff. One second after it has left your hand, its vertical distance below the top of the cliff is

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5 m.

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Throw an object upward at a 45 degree angle. With no gravity it will follow a straight-line path. But because of gravity, at the end of 1 second, it is

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about 5 m below the straight line.

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Roll a bowling ball off the edge of a table. As it falls, its horizontal component of velocity

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remains constant.

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A bullet fired horizontally from a rifle begins to fall

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as soon as it leaves the barrel.

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A projectile is launched vertically upward at 50 m/s. If air resistance is negligible, its speed upon returning to its starting point is

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50 m/s.

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An Earth satellite is simply a projectile

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freely falling around the Earth.

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Earth satellites are typically more than 100 km high so as to be above the Earth’s

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atmosphere.

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A projectile is fired horizontally in a region of no air resistance. The projectile maintains its horizontal component of velocity because

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it is not acted on by any horizontal forces.

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A hunter on level ground fires a bullet at an angle of 10 degrees above the horizontal while simultaneously dropping another bullet from the level of the rifle. Which bullet will hit the ground first?

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the dropped one

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A hunter on level ground fires a bullet at an angle of 2 degrees below the horizontal while simultaneously dropping another bullet from the level of the rifle. Which bullet will hit the ground first?

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the fired one

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A bullet fired horizontally over level ground hits the ground in 0.5 second. If it had been fired with twice the speed in the same direction, it would have hit the ground in

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0.5 s.

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An object is dropped and freely falls to the ground with an acceleration of 1 g. If it is thrown upward at an angle instead, its acceleration will be

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1 g downward.

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A projectile is launched at ground level an angle of 15 degrees above the horizontal and lands down range. What other projection angle for the same speed would produce the same down-range distance?

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75 degrees

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A projectile is fired into the air at an angle of 50 degrees with the ground and lands on a target that is at the same level at which the projectile started. It will also land on the target if it is fired at an angle of

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40 degrees.

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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 second later?

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100

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Two projectiles are fired from ground level at equal speeds but different angles. One is fired at an angle of 30 degrees and the other at 60 degrees. The projectile to hit the ground first will be the one fired at (neglect air resistance)

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30 degrees.

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After a rock thrown straight up reaches the top of its path and then falls a short distance, its acceleration is (neglect air resistance)

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the same as it was at the top of its path.

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A projectile is fired vertically from the surface of the Earth at 8 km/s. The projectile will

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rise and fall back to the Earth’s surface.

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The ground speed of an airplane that has an airspeed of 200 km/h when it is in a 200-km/h crosswind is

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283 km/h.

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Without air resistance, a projectile fired horizontally at 8 km/s from atop a mountain would

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accelerate downward at g as it moves horizontally; trace a curve that matches the earth’s curvature; and return later to its starting position and repeat its falling behavior.

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Acceleration due to gravity on the moon is less than on Earth, and the moon is smaller than Earth. So compared to an Earth satellite, a satellite in close orbit about the moon would travel

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slower.

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An object is thrown vertically into the air. Because of air resistance, the time for its descent will be

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longer than the ascent time.

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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?

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about 20 m/s

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An airplane flies at 40 m/s at an altitude of 50 meters. The pilot drops a heavy package which falls to the ground. Where, approximately, does the package land relative to the plane’s new position?

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beneath the plane

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A bullet is fired horizontally with an initial velocity of 300 m/s from a tower 20 m high. If air resistance is negligible, the horizontal distance the bullet travels before hitting the ground is about

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600 m

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A river 100 m wide flows due south at 1 m/s. A boat that goes 1 m/s relative to the water is pointed due east as it crosses from the west bank. The boat reaches the east bank

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100 m farther south than where it started.

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A river 100 m wide flows due south. A boat that goes 1 m/s relative to the water is pointed due east as it crosses from the west bank. Relative to the Earth, the boat travels

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141 m.

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A river 100 m wide flows due south. A boat that goes 1 m/s relative to the water is pointed due east as it crosses from the west bank. The boat crosses in

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100 s.

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A river 100 m wide flows due south at 1 m/s. A boat that goes 1 m/s relative to the water leaves the west bank. To land at a point due east of its starting point, the boat must be pointed

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nowhereâ€”it can’t be done.

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The tangential velocity of an Earth satellite is its velocity

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parallel to the surface of the Earth.

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The radial velocity of an Earth satellite is its velocity

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perpendicular to the surface of the Earth.

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If a satellite’s radial velocity is zero at all times, its orbit must be

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circular.

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Planets would crash into the sun if it weren’t for

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their tangential velocities.

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What prevents satellites such as the space shuttle from falling?

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Nothing; they are continually falling as they orbit the Earth.

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The circular path of a satellite orbiting the Earth is characterized by a constant

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speed; acceleration; and radial distance.

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An Earth satellite is in an elliptical orbit. The satellite travels fastest when it is

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nearest the Earth.

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The fastest moving planet in a solar system is

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the planet nearest the sun.

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It takes Pluto a longer time to orbit the sun than the Earth does because Pluto

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Choices A and B are both correct

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A woman on the surface of the Earth has a mass of 50 kilograms and a weight of 490 newtons. If the woman were floating freely inside a space habitat far away from Earth, she would have

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less weight and the same mass.

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A “weightless” astronaut in an orbiting shuttle is

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like the shuttle, pulled by Earth’s gravitation.

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Consider a moon that orbits one of our most distant planets in an elliptical path. The distance that the moon covers each day is

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greatest when the moon is closest to the planet.

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A satellite describes an elliptical orbit about a planet. The satellite travels much faster when it is directly over a

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None of the above choices affects its speed very much.

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Our moon travels the fastest as it orbits the Earth when it is

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closest.

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A lunar month is about 28 days. If the moon were farther from the Earth than it is now, the lunar month would be

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more than 28 days.

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A lunar month is about 28 days. If the moon were closer to the Earth than it is now, the lunar month would be

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less than 28 days.

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The speeds of the planets about the sun depend on

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their distances from the sun.

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A projectile is fired vertically from the surface of the Earth at 5 km/s. The projectile will

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rise and fall back to the Earth’s surface.

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A vertically oriented rocket that is somehow able to maintain a continuous upward velocity of 8 km/s will

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escape from the Earth.

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Consider a monkey wrench released at rest at the far edge of the solar system. Suppose that it drops to the Earth by virtue of only Earth gravity. It will strike the Earth’s surface with a speed of about

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11.2 km/s.

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Minimal orbital speed about the Earth is about 8 km/s. Minimal orbital speed about the moon would be

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less than 8 km/s.

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Minimal orbit speed about the Earth is about 8 km/s. Minimal orbital speed about Jupiter would be

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more than 8 km/s.

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A satellite in an elliptical orbit travels at constant

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None of these.

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The period of a satellite, the time it takes for a complete revolution, depends on the satellite’s

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radial distance.

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A satellite near the Earth makes a full circle in about an hour and a half. How long would a satellite located as far away as the moon take to orbit the Earth?

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about 28 days

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The Early Bird communication satellite hovers over the same point on Earth’s equator indefinitely. This is because

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its orbital period is 24 hours.

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Communications and weather satellites always appear at the same place in the sky. This is because these satellites are

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orbiting the Earth with a 24-hour period.

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Compared to the period of satellites in orbit close to the Earth, the period of satellites in orbit far from the Earth is

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longer.

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Pioneer 10 was able to escape the solar system by

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bouncing off” Jupiter like a tennis ball bouncing off an approaching tennis racket.

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From Earth, one satellite appears to overtake another. The faster satellite is

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lower.

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Rockets that launch satellites into orbit need less thrust when fired from

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Hawaii

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The force of gravity does work on a satellite when it is in

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elliptical orbit.

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Angular momentum is conserved for a satellite in

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circular orbit; and elliptical orbit.

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Acceleration is greater for a satellite when it is at the

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perigee.

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Angular momentum is greater for a satellite when it is at the

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same at apogee and perigee

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Which would require the greater change in the Earth’s orbital speed (30 km/s); slowing down so the Earth crashes into the sun, or speeding up so the Earth escapes the sun?

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slowing down

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Which would require the greater energy; slowing down of the orbital speed of the Earth so it crashes into the sun, or speeding up the orbital speed of the Earth so it escapes the sun?

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speeding up

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A rocket coasts in an elliptical orbit about the Earth. To attain escape velocity using the least amount of fuel in a brief firing time, should it fire off at the apogee, or at the perigee? (Hint: Let “Fd = change in KE” guide your thinking.)

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perigee, where it is closest and fastest