PSI CH 04 Homework

Exercise 4.95 If a space vehicle circled Earth at a distance equal to the Earth-Moon distance, how long would it take for it to make a complete orbit? In other words, what would be its period?

28 days

Exercise 4.103 Earth is farther away from the Sun in June and closest in December. In which of these two months is Earth moving faster around the Sun? A) The Earth travels faster about the Sun in December than in June. B) The traveling speed of the Earth about the Sun always is the same. C) The Earth travels faster about the Sun in June than in December.

A) The Earth travels faster about the Sun in December than in June.

Video Tutor: Ball Fired Upward from Accelerating Cart Consider the video you just watched. Suppose we replace the original launcher with one that fires the ball upward at twice the speed. We make no other changes. How far behind the cart will the ball land, compared to the distance in the original experiment? A) four times as far B) the same distance C) half as far D) twice as far E) by a factor not listed above

A) four times as far

Exercise 4.64 Consider a space pod somewhere between Earth and the Moon, at just the right distance so that the gravitational attractions to Earth and the Moon are equal. Is this location nearer Earth or the Moon? A) nearer the Moon B) nearer the Earth

A) nearer the Moon

Video Tutor: Dropped and Thrown Balls Which ball (if either) has the greatest speed at the moment of impact? A) The dropped ball B) The ball thrown horizontally C) Both balls have the same speed.

B) The ball thrown horizontally

Reading Check 4.12 What was the cause of perturbations discovered in the orbit of planet Uranus? A) gravitational pulls from Pluto B) gravitational pulls from Neptune C) gravitational pulls from the Earth D) gravitational pulls from the nearest star proxima centauri

B) gravitational pulls from Neptune

Reading Check 4.8 Would the springs inside a bathroom scale be more compressed or less compressed if you weighed yourself in an elevator that accelerated upward? Accelerated downward? A) upward, less compressed; downward, more compressed B) upward, more compressed; downward, more compressed C) upward, less compressed; downward, less compressed D) upward, more compressed; downward, less compressed

D) upward, more compressed; downward, less compressed

Plug and Chug 4.37 F = G m1m2/d^2 Calculate the force of gravity on the 1.2-kg mass if it were 6.4×10^6 m above Earth's surface (that is, if it were two Earth radii from Earth's center).

F = 2.9 N

Think and Rank 4.58 Rank the average gravitational forces from greatest to least between (a) the Sun and Mars, (b) the Sun and the Moon, and (c) the Sun and Earth.

GREATEST: C ; A ; B :LEAST

Think and Solve 4.51 A satellite at a particular point along an elliptical orbit has a gravitational potential energy of 5000 MJ with respect to Earth's surface and a kinetic energy of 4000 MJ . Later in its orbit the satellite's potential energy is 5800 MJ. Use conservation of energy to find its kinetic energy at that point.

K = 3200 MJ

Visual Activity: Exploring a Person's Weight in a Moving Elevator Part A: Suppose you are in an elevator. As the elevator starts upward, its speed will increase. During this time when the elevator is moving upward with increasing speed, your weight will be __________. A) greater than your normal weight at rest B) equal to your normal weight at rest C) less than your normal weight at rest Part B: Suppose you are in an elevator that is moving upward. As the elevator nears the floor at which you will get off, its speed slows down. During this time when the elevator is moving upward with decreasing speed, your weight will be __________. A) greater than your normal weight at rest B) equal to your normal weight at rest C) less than your normal weight at rest Part C: As you found in Part A, your weight will be greater than normal when the elevator is moving upward with increasing speed. For what other motion would your weight also be greater than your normal weight? A) The elevator moves upward with constant velocity. B) The elevator moves downward with constant velocity. C) The elevator moves upward while slowing in speed. D) The elevator moves downward while slowing in speed. E) The elevator moves downward while increasing in speed. Part D: If you are standing on a scale in an elevator, what exactly does the scale measure? A) your mass B) the force you exert on the scale C) the gravitational force exerted on you by Earth

Part A: A) greater than your normal weight at rest Part B: C) less than your normal weight at rest Part C: D) The elevator moves downward while slowing in speed. Part D: B) the force you exert on the scale

Video: Projectile Motion Part A: When Dr. Hewitt releases the two projectiles, which one hits the ground first? A) The ball that goes horizontally hits the ground first. B) The ball that drops vertically hits the ground first. C) Both balls hit the ground at the same time. Part B: Why do the two objects hit the table at the relative times that they do? A) Gravity pulls the same amount on each ball, and they each drop the same distance. B) The ball that is shot horizontally travels a longer path in the air. C) The inertia of the ball that is shot horizontally makes it less susceptible to gravity.

Part A: C) Both balls hit the ground at the same time. Part B: A) Gravity pulls the same amount on each ball, and they each drop the same distance.

Mass versus Weight Part A: Consider an object of mass 45 kg. Rank the weight of this object at the following locations. Heaviest to lightest Part B: What would be the weight of an object on Jupiter if the object weighs 1.7 lb on Mars? Part C: What would be the mass of an object on Jupiter if the object has a mass of 1.7 kg on Mars?

Part A: Jupiter, Earth, Saturn, Mars, Moon Part B: Weight on Jupiter = 11 lb Part C:

Ranking Task: Gravity and Newton's Laws Part A: The following five diagrams show pairs of astronomical objects that are all separated by the same distance d. Assume the asteroids are all identical and relatively small, just a few kilometers across. Considering only the two objects shown in each pair, rank the strength, from strongest to weakest, of the gravitational force acting on the asteroid on the left. Part B: The following diagrams are the same as those from Part A. Again considering only the two objects shown in each pair, this time rank the strength, from strongest to weakest, of the gravitational force acting on the object on the right. Part C: The following diagrams are the same as those from Part A. This time, rank the pairs from left to right based on the size of the acceleration the asteroid on the left would have due to the gravitational force exerted on it by the object on the right, from largest to smallest. Part D: Consider Earth and the Moon. As you should now realize, the gravitational force that Earth exerts on the Moon is equal and opposite to that which the Moon exerts on Earth. Therefore, according to Newton's second law of motion __________. A) the Moon has a larger acceleration than Earth, because it has a smaller mass B) Earth has a larger acceleration than the Moon, because it has a larger mass C) the Moon and Earth both have equal accelerations, because the forces are equal

Part A: asteroid-sun ; asteroid-earth ; asteroid-moon ; asteroid-asteroid ; asteroid-hydrogen atom Part B: asteroid-sun ; asteroid-earth ; asteroid-moon ; asteroid-asteroid ; asteroid-hydrogen atom Part C: asteroid-sun ; asteroid-earth ; asteroid-moon ; asteroid-asteroid ; asteroid-hydrogen atom Part D: A) the Moon has a larger acceleration than Earth, because it has a smaller mass

Think and Solve 4.53 A baseball is tossed at a steep angle into the air and makes a smooth parabolic path. Its time in the air is t, and it reaches a maximum height h. Assume that air resistance is negligible. Part A: Find the height reached by the ball. Part B: If the ball is in the air for 3.4 s , find a height it reaches. Part C: If the ball reached the same height as when tossed at some other angle, would the time of flight be the same?

Part A: h = gt^2/8 Part B: h = 14 m Part C: yes

Think and Solve 4.42 Suppose you stood on top of a ladder that was so tall that you were two times as far from Earth's center as you presently are. What would be your weight from its present value?

Wtop/Wpres = 0.25