PHY 101: Ch. 9/10 Homework and Quiz

Suppose the height of the net is 1.05 m, and the court's border is 13.0 m from the bottom of the net. Use g=10 m/s^2 and find the maximum speed of the horizontally moving ball clearing the net.

13/square root (2*1.05)/10 = 28m/s

At a particular point in orbit a satellite in an elliptical orbit has a gravitational potential energy of 4900 MJ with respect to Earth's surface and a kinetic energy of 5000 MJ. Later in its orbit, the satellite's potential energy is 6000 MJ.

4900+5000= 9900 9900-6000 = 3900 MJ

At a particular point in orbit a satellite in an elliptical orbit has a gravitational potential energy of 5500 MJ with respect to Earth's surface and a kinetic energy of 4500 MJ. Later in its orbit, the satellite's potential energy is 6000 MJ. What is its Kinetic Energy at that point?

5500+4500 = 10000 MJ 10000-6000 = 4000 MJ

The magnitude of g at Earth's surface is about 9.8 m/s^2. What is the value of g at a distance of twice Earth's radius?

9.8/4 = 2.45 m/s^2

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

B. rise and fall back to the Earth's surface.

How does the thickness of paint sprayed on a surface change when the sprayer is held twice as far away? A. It is ¼ as thick. B. It is ½ as thick. C. It is twice as thick. D. It is the same thickness.

C. It is twice as thick.

What is the magnitude of Earth's gravitational force on a 1-kg body at Earth's surface? A. 6.67 × 10^-11 N B. 1 kg C. 6.67 × 10^-11 kg D. 10 N

D. 10 N

Find the change in the gravitational force between two planets if the masses of both planets are doubled but the distance between them stays the same. (F new/F)

Fnew/F = 4

Why doesn't the force of gravity change the speed of a satellite in circular orbit? a. The force is at a right angle to the velocity. b. The inertia of the fast satellite is so great that gravity can be ignored. c. Air resistance counteracts the effects of gravity. d. Satellites orbit at a height where gravity is essentially zero.

a. 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? a. The force of gravity is perpendicular to the motion in a circular orbit but not in an elliptical orbit. b. Kinetic energy is constant for both orbits. c. The force of gravity is perpendicular to the motion in an elliptical orbit but not in a circular orbit. d. Kinetic energy is not constant for a satellite in a circular orbit but it is for a satellite in an elliptical orbit.

a. The force of gravity is perpendicular to the motion in a circular orbit but not in an elliptical orbit

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 a. about 5 m below the straight line. b. about 15 m below the straight line. c. about 10 m below the straight line.

a. about 5 m below the straight line.

Earth is closer to the Sun in December than in June. In which of these two months is Earth moving faster around the Sun? a. in December b. in June

a. in December

An Earth satellite in an elliptical orbit travels fastest when it is a. nearest Earth. b. farthest from Earth. c. everywhere along its orbit.

a. nearest Earth.

Tidal forces in general are the result of a. unequal forces acting on different parts of a body. b. the inverse-square law. c. a combination of any kind of forces acting on a body. d. two or more sources of gravitation. e. unequal fluid flow.

a. unequal forces acting on different parts of a body

Is gravitational force acting on a person who falls off a cliff? a. yes b. no

a. yes

Two projectiles are fired from ground level at equal speeds but different angles. One is fired at an angle of 30° and the other at 60°. Neglecting air resistance, the projectile to hit the ground first will be the one fired at a. both hit at the same time b. 30°. c. 60°.

b. 30°.

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 a. 60 degrees. b. 40 degrees. c. 55 degrees. d. 45 degrees. e. none of these

b. 40 degrees

How does the force of gravity between two bodies change when the distance between them is doubled? a. The force doubles. b. The force decreases to ¼ of its initial value. c. The force is cut in half. d. The force quadruples.

b. The force decreases to ¼ of its initial value.

An Earth satellite is simply a projectile a. floating motionless in space near the Earth. b. freely falling around the Earth. c. approaching the Earth from outer space.

b. freely falling around the Earth.

When the distance between two stars decreases by one-third, the force between them a. decreases by one-half. b. increases to nine times as much. c. decreases by one-third. d. increases to twice as much. e. none of the above

b. increases to nine times as much.

When the potential energy of a satellite decreases a. its distance from the orbiting body increases. b. its kinetic energy correspondingly increases. c. kinetic energy also decreases. d. none of the above

b. its kinetic energy correspondingly increases.

Is there change in the force of gravity between two objects when their masses are doubled and the distance between them is also doubled? a. yes b. no

b. no

Acceleration is greater for a satellite when it is at the a. zenith. b. perigee (closest point). c. apogee (farthest point). d. same acceleration at all of the above places.

b. perigee (closest point).

Inside a freely-falling runaway elevator, your a. acceleration is zero. b. weight is zero. c. gravitational interaction with Earth is zero. d. all of the above e. none of the above

b. weight is zero

Is gravitational force acting on an astronaut inside an orbiting space shuttle? a. no b.yes

b. yes

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? a. 50 m b. 98 m c. 100 m d. 490 m e. none of these

c. 100 m

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 a. 10 m. b. 15 m. c. 5 m.

c. 5 m

How far does a projectile drop in 1 second? What is the speed needed for a projectile to orbit Earth? a. 20 m, 32 km/s b. 10 m, 16 km/s c. 5 m, 8 km/s d. 1 m, 1.6 km/s

c. 5 m, 8 km/s

Is the sum of kinetic and potential energies a constant for satellites in circular orbits, in elliptical orbits, or in both? a. Neither b. Circular only c. Both d. Elliptical only

c. Both

If the sun were twice as massive a. the pull of the Earth on the sun would double. b. its pull on the Earth would double. c. both of these d. neither of these

c. both of these

If the radius of the Earth somehow decreased with no change in mass, your weight would a. not change. b. decrease. c. increase.

c. increase

If your mass, the mass of the Earth, and the mass of everything in the solar system were twice as much as it is now, yet everything stayed the same size, your weight on Earth would a. double. b. be the same. c. quadruple. d. be eight times as much as now. e. none of these

c. quadruple

An Earth satellite in an elliptical orbit has its smallest speed a. closest to Earth. b. when getting farther from Earth. c. when farthest from Earth. d. need more information

c. when farthest from Earth.

The circular path of a satellite orbiting Earth is characterized by a constant a. acceleration. b. radial distance. c. speed. d. all of the above e. none of the above

d. all of the above

Without air resistance, a projectile fired horizontally at 8 km/s from atop a mountain would a. trace a curve that matches the earth's curvature. b. return later to its starting position and repeat its falling behavior. c. accelerate downward at g as it moves horizontally. d. all of these e. none of these

d. all of these

According to Kepler's laws, the paths of planets about the sun are a. circles. b. straight lines. c. parabolas. d. ellipses. e. none of these

d. ellipses

If Earth shrank, but there was no change in its mass, then what would happen to your weight at the surface? a. It would decrease at first and then increase. b. It would decrease. c. It would stay the same. d. It would increase.

d. it would increase

You're in an airplane that flies horizontally with speed 1000 km/h (290 m/s) when an engine falls off. Neglecting air resistance, assume it takes 25 s for the engine to hit the ground. Find the horizontal distance that the aircraft engine falls.

v = d/t 290 = d/25 d = 7250

Which has the higher tides: spring tides or neap tides? Why? A. Spring tides are higher, because the tides from the Moon and Sun add together. B. Neap tides are higher, because the tides from the Moon and Sun partially cancel. C. Neap tides are higher, because the tides from the Moon and Sun add together. D. Spring tides are higher, because the tides from the Moon and Sun partially cancel.

A. Spring tides are higher, because the tides from the Moon and Sun add together.

Why are all tides greatest at the time of a full Moon or new Moon? A. At full Moon and new Moon, the tides from the Moon and the Sun add because they make a right angle with Earth. B. At full Moon and new Moon, the tides from the Moon and the Sun add because they are in line with Earth. C. At full Moon and new Moon, the tides from the Moon and the Sun partially cancel because they are in line with Earth. D. At full Moon and new Moon, the tides from the Moon and the Sun partially cancel because they make a right angle with Earth.

B. At full Moon and new Moon, the tides from the Moon and the Sun add because they are in line with 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? A. It decreases while rising and while falling. B. It decreases while rising, but it increases while falling. C. It increases while rising, but it decreases while falling. D. Rising or falling, it does not change.

B. It decreases while rising, but it increases while falling.

Where do you weigh more: at the bottom of Death Valley or atop one of the peaks of the Sierra Nevada? Why? A. You weigh more in Death Valley because more atmosphere pushes down on you. B. You weigh more in Death Valley because you are closer to the center of Earth. C. You weigh more on the summit, because the higher you go, the harder you fall. D. You weigh more on the summit because the air buoys you up less.

B. You weigh more in Death Valley because you are closer to the center of Earth.

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? a. 10 m, 20 m b. 5 m, 20 m c. 5 m, 10 m d. 10 m, 40 m

b. 5 m, 20 m

You're in an airplane that flies horizontally with speed 1000 km/h, (290 m/s) when an engine falls off. Neglecting air resistance, assume it takes 25 s for the engine to hit the ground. Find the height of airplane.

d = V1 + (1/2)*a*change in t^2 d = 0 + (1/2)*10*25^2 = 3125 m

How far below a straight-line path does a horizontally projected projectile fall in the first second of fall? a. 10 meters b. Zero meters c. Depends on the projected speed d. 5 meters

d. 5 meters

A projectile is launched from ground level at 15° above the horizontal and lands downrange. What other projection angle for the same speed would produce the same down-range distance? a. 30° b. 90° c. 50° d. 75° e. 45°

d. 75°