Chapter 4

Which of the following quantities would be acceptable representations of weight?

12.0 lbs 1600 kN 899 MN Weight is a force and is measured in newtons (or kilonewtons, meganewtons, etc.) or in pounds (or tons, megatons, etc.).

Rank gravitational forces from greatest to least.

Greatest to least Greatest A then B then C then D least Closest to the planet is greatest gravitational force.

If the acceleration due to gravity on the earth is 9.8 m/s2, what is the acceleration due to gravity on Rams?

5.7 m/s2

Rank from greatest to least their orbital speeds.

Greatest A Middle B Least C (smallest to largest)

Which projectile spends more time in the air, the one fired from 30∘∘ or the one fired from 60∘∘?

The one fired from 60^o The projectile fired from 60∘∘ has a greater vertical velocity than the one fired from 30∘∘, so it spends more time in the air.

Is the period longer or shorter for orbits of higher altitude?

longer

After Punch Taut travels to Pentune, what actually happens to his mass and his weight?

mass remains the same; weight decreases

Which planet should Punch travel to if his goal is to weigh in at 118 lb? Refer to the table of planetary masses and radii given to determine your answer.

Pentune

What is the status of Pluto in the family of planets?

dwarf planet

Using the universal law of gravity, we can find the weight of an object feeling the gravitational pull of a nearby planet. We can write an expression w=GmM/r2w=GmM/r2, where w is the weight of the object, G is the gravitational constant, mmm is the mass of that object, M is mass of the planet, and r is the distance from the center of the planet to the object. If the object is on the surface of the planet, r is simply the radius of the planet. The gravitational field on the surface of the earth is stronger than that on the surface of the moon. If a rock is transported from the moon to the earth, which properties of the rock change?

weight only

To understand the distinction between mass and weight and to be able to calculate the weight of an object from its mass and Newton's law of gravitation. The concepts of mass and weight are often confused. In fact, in everyday conversations, the word "weight" often replaces "mass," as in "My weight is seventy-five kilograms" or "I need to lose some weight." Of course, mass and weight are related; however, they are also very different.Mass, as you recall, is a measure of an object's inertia (ability to resist acceleration). Newton's 2nd law demonstrates the relationship among an object's mass, its acceleration, and the net force acting on it: Fnet=maFnet=ma. Mass is an intrinsic property of an object and is independent of the object's location.Weight, in contrast, is defined as the force due to gravity acting on the object. That force depends on the strength of the gravitational field of the planet: w=mgw=mg, where www is the weight of an object, mmm is the mass of that object, and ggg is the local acceleration due to gravity (in other words, the strength of the gravitational field at the location of the object). Weight, unlike mass, is not an intrinsic property of the object; it is determined by both the object and its location. Which of the following quantities represent mass?

.34 g 120 kg

An object is lifted from the surface of a spherical planet to an altitude equal to the radius of the planet. As a result, which of the following changes in the properties of the object take place?

mass remains the same; weight decreases

If you are standing on a scale in an elevator, what exactly does the scale measure?

the force you exert on the scale You probably recognize that neither your mass nor the gravitational force exerted on you change when you are in an elevator. The scale measures the force that is exerted on it, which in an elevator is a combination of the force due to your normal weight and a force due to the elevator's acceleration.

An astronaut lands on a planet that has the same mass as Earth but half the diameter. How does the astronaut's weight differ from that on Earth?

Astronaut has four times as much weight as on Earth.

Punch Taut is a down-on-his-luck heavyweight boxer. One day, he steps on the bathroom scale and "weighs in" at 236 lb. Unhappy with his recent bouts, Punch decides to go to a different planet where he would weigh in at 118 lb so that he can compete with the bantamweights who are not allowed to exceed 118 lb. His plan is to travel to Xobing, a newly discovered star with a planetary system. Here is a table listing the planets in that system: In this table, the mass and the radius of each planet are given in terms of the corresponding properties of the earth. For instance, Tehar has a mass equal to 2.1 earth masses and a radius equal to 0.80 earth radii. If acceleration due to gravity on the earth is ggg, which formula gives the acceleration due to gravity on Loput?

(5.6) -------- ( G) 1.7^2

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?

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

According to the video of throwing two balls from a ladder, Which ball (if either) has the greatest speed at the moment of impact?

The ball thrown horizontally The two balls have the same vertical velocity when they land, but the thrown ball has an additional horizontal velocity component. Since speed is defined as the magnitude of the resultant velocity vector, the thrown ball is moving faster when it lands.

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?

The elevator moves downward while slowing in speed. When the elevator is moving downward, a downward acceleration would mean an increasing downward speed. Therefore, as your answer correctly states, an upward acceleration would mean a decreasing downward speed.

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 __________.

greater than your normal weight at rest Increasing speed means acceleration, and when the elevator is accelerating upward you will feel a force pressing you to the floor, making your weight greater than your normal (at rest) weight.

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 __________.

less than your normal weight at rest Even though the elevator is still moving upward, the fact that its speed is slowing means that the acceleration is downward; the situation is rather like that of a ball that is still on its way up after you throw it, even though it is being pulled downward with the acceleration of gravity. Because the acceleration of the elevator is downward, your weight is lower than normal.