PHSC 1001- Ch. 9 MasteringPhysics

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

A

Tidal forces in general are the result of A. unequal forces acting on different parts of a body. B. the inverse-square law. C. two or more sources of gravitation. D. unequal fluid flow. E. a combination of any kind of forces acting on a body.

A

What is the magnitude of the gravitational force between two 1-kg bodies that are 1 m apart? A. 6.67 × 10 -11 N B. 1 kg C. 10 N D. 6.67 × 10 -11 kg

A

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.

According to Newton's second law, the asteroid with the largest acceleration will be the one that has the strongest gravitational force exerted on it by the object on the right. That is why the ranking here is the same as the ranking for Part A.

The constant G in Newton's equation _______. A. shows gravity to be a relatively huge force B. makes the units of measurement consistent C. was measured by Newton D. produces equilibrium

B

The force of Earth's gravity on a capsule in space will lessen as it moves farther away. If the capsule moves to twice its distance, the force toward Earth becomes A. three-quarters. B. one-fourth. C. half. D. none of the above

B

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.

Because the distance is the same for all five cases, the gravitational force depends only on the product of the masses. And because the same asteroid is on the left in all five cases, the relative strength of gravitational force depends on the mass of the object on the right. Continue to Part B to explore what happens if we instead ask about the gravitational force acting on the object on the right.

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. B. It would decrease at first and then increase. C. It would increase. D. It would stay the same.

C

What would the magnitude of the gravitational field be anywhere inside a hollow, spherical planet? A. The same as the surface value B. A quarter of the surface value C. Half the surface value D. Zero N/kg

D

Calculate the force of gravity on the 1-kg mass if it were 6.4×106 m above Earth's surface (that is, if it were two Earth radii from Earth's center). F=G([m1m2)/d^2]

F = 2.4N

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

Fnew/F = 4

Each of the following diagrams shows a spaceship somewhere along the way between Earth and the Moon (not to scale); the midpoint of the distance is marked to make it easier to see how the locations compare. Assume the spaceship has the same mass throughout the trip (that is, it is not burning any fuel). Rank the five positions of the spaceship from left to right based on the strength of the gravitational force that Earth exerts on the spaceship, from strongest to weakest.

Gravity follows an inverse square law with distance, which means the force of gravity between Earth and the spaceship weakens as the spaceship gets farther from Earth.

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.

Newton's third law tells us that the gravitational force exerted on the asteroid on the left by the object on the right will be exactly the same as the gravitational force exerted on the object on the right by the asteroid on the left. That is why the ranking here is the same as the ranking for Part A.

The following diagrams show five pairs of asteroids, labeled with their relative masses (M) and distances (d) between them. For example, an asteroid with M=2 has twice the mass of one with M=1 and a distance of d=2 is twice as large as a distance of d=1. Rank each pair from left to right based on the strength of the gravitational force attracting the asteroids to each other, from strongest to weakest.

You have correctly taken into account both the masses of the asteroids and the distances between them

What happens to the strength of the gravitational field at the surface of a star that shrinks? A. It stays the same. B. It increases. C. It decreases. D. It first increases and then it decreases.

B

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 partially cancel because they are in line 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 add because they make a right angle 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

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 on the summit, because the higher you go, the harder you fall. B. You weigh more in Death Valley because more atmosphere pushes down on you. C. You weigh more in Death Valley because you are closer to the center of Earth. D. You weigh more on the summit because the air buoys you up less.

C

The following diagrams are the same as those from Part A. This time, rank the five positions of the spaceship from left to right based on the strength of the gravitational force that the Moon exerts on the spaceship, from strongest to weakest.

Gravity follows an inverse square law with distance, which means the force of gravity between the Moon and the spaceship increases as the spaceship approaches the Moon. Now continue to Part C for activities that look at the effects of both distance and mass on gravity.