16. When a bullet is fired from a rifle: mine is D

A. the recoiling rifle and the bullet have the same kinetic energy and momentum
B. the bullet has greater momentum and kinetic energy than the rifle
C. the rifle has greater momentum and kinetic energy than the bullet
D. they have the same momentum, but the bullet has greater kinetic energy than the rifle

17. If earth's mass decreased to one-half its original mass with no change in radius, then your weight would: mine is B
A. stay the same
B. decrease to 1/2 your original weight
C. decrease to one-quarter your original weight
D. double your original weight

18. When the distance between two stars decreases by half, the force between them: mine is a
A. increases to four timees as much
B. increases to twice as much
C. decreases to 1/2
D. decreases by one-quarter

19. Two objects move towards each other because of gravity. As the objects get closer and closer, the acceleration of each: mine is B
A. decreases because the force decreases
B. stasy the same because the force stays the same
C. increases due to increased force between them
D. decreases due to increased momentum in opposite directions.

20. During an eclipse of the sun (when earth, moon, and sun are lined up), the ocean tides on earth are extra ____ and are called ____ tides. Mine is B
A. low, spring
B. high, spring
C. low, neap
D. high, neap

To answer these questions, we need to understand some basic principles of physics. Let's go through each question and explain how to arrive at the correct answer.

16. When a bullet is fired from a rifle:
Here, we are asked about the kinetic energy and momentum comparison between the bullet and the rifle. To determine the answer, we need to consider the conservation of momentum. When the bullet is fired, it exerts force on the rifle in the opposite direction. This results in both the bullet and the rifle moving. According to the conservation of momentum, the total momentum before and after the event should be the same. However, kinetic energy depends on the mass and velocity of the objects. So, the bullet might have a greater kinetic energy than the rifle. Thus, the correct answer is D: they have the same momentum, but the bullet has greater kinetic energy than the rifle.

17. If Earth's mass decreased to one-half its original mass with no change in the radius, then your weight would:
In this question, we need to understand the relationship between mass, weight, and gravitational force. Weight is directly proportional to mass, as well as the gravitational force acting on an object. When mass decreases, the weight decreases as well. Since the Earth's mass is reduced to one-half, your weight would decrease to 1/2 your original weight. Therefore, the correct answer is B: decrease to 1/2 your original weight.

18. When the distance between two stars decreases by half, the force between them:
To answer this question, we need to consider Newton's Law of Universal Gravitation, which states that the force between two objects is inversely proportional to the square of the distance between their centers. So, if the distance is reduced by half, the force between them would increase. Specifically, the force would increase to four times the original force because the change in distance is squared. Therefore, the correct answer is A: increases to four times as much.

19. Two objects move towards each other because of gravity. As the objects get closer and closer, the acceleration of each:
This question asks about the behavior of acceleration as two objects move closer due to gravity. Gravity is an attractive force that causes acceleration. As the objects get closer, the force of gravity between them increases. According to Newton's second law, acceleration is directly proportional to force and inversely proportional to mass. Therefore, the acceleration will increase due to the increased force acting between the objects. So, the correct answer is C: increases due to the increased force between them.

20. During an eclipse of the sun (when Earth, Moon, and Sun are lined up), the ocean tides on Earth are extra ____ and are called ____ tides.
In this question, we need to understand the relationship between tides and the alignment of celestial bodies. During an eclipse when the Earth, Moon, and Sun are lined up, the gravitational pull of the Moon and the Sun combines, creating extra-high tides. These tides are called spring tides. Therefore, the correct answer is B: high, spring.