Identify several of the forces that are acting on or around you. (select all that apply.)

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The Physics Classroom » The Rewatch Session » Newton's Laws of Motion » Answers Q#8-28
Newton's Laws of Motion Review

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Recheck out Session Home - Topic ListingNewton's Laws - Home || Printable Version || Questions via LinksAnswers to Questions: All || #1-7 || #8-36 || #37-46 || #47-60

Part C: Forced Choice and also Brief Answer

8a. Big Bubba has a mass of 100 kg on the earth. What is Big Bubba's mass on the moon where the pressure of gravity is roughly 1/6-th that of Earth's? ________ Explain or present your work-related.

You watching: Identify several of the forces that are acting on or around you. (select all that apply.)

Answer: 100 kg

Mass is a amount which is independent of the place of the object. So if Big Bubba has a mass of 100 kg on Planet, then he also has actually a mass of 100 kg on the moon. Only the weight would certainly adjust as Big Bubba is moved from the Earth to the moon. He weighs ~1000 N on Earth and also 1/6-th this worth (~167 N) on the moon.

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8b. Little Billie weighs 360 N on Earth. What is Little Billie's mass on the moon wbelow the force of gravity is approximately 1/6-th that of Earth's? ________ Exordinary or display your occupational.

Answer: ~36 kg

The mass of an item is pertained to weight by the equation W = m•g wright here g = ~10 m/s/s on Planet and one-sixth this value (~1.67) on the moon. So if Billy weighs 360 N on Planet, then his mass is roughly ~36 kg. His mass on the moon will be the very same as his mass on Planet. Only his weight changes once on the moon; quite than being 360 N, it is 60 N. His weight on the moon could be discovered by multiplying his mass by the worth of g on the moon: (36 kg) • (9.8/6 m/s/s) = ~60 N

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9. TRUE or FALSE:

An object which is moving rightward has a rightward pressure acting upon it.

Answer: False

An object which is increasing rightward have to have actually a rightward pressure and a rightward net pressure acting upon it. But an object which is merely relocating rightward does not necessarily have a rightward pressure upon it. A automobile that is moving rightward and skidding to a sheight would certainly not have a rightward force acting upon it.

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10. The amount of net pressure required to save a 5-kg object moving rightward through a constant velocity of 2 m/s is ____.

a. 0 N

b. 0.4 N

c. 2 N

d. 2.5 N

e. 5 N

Answer: A

Net force is constantly m•a. In this instance, the velocity is continuous so the acceleration is zero and the net force is zero. Constant velocity activity have the right to constantly be connected with a zero net force.

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11. TRUE or FALSE:

For an object relaxing upon a non-accelerating surface, the normal pressure is equal to the weight of the object.

Answer: False

Quite surprisingly to many, the normal force is not necessarily constantly equal to the weight of an object. Suppose that a perboy weighs 800 N and sits at rest upon a table. Then mean another perkid comes along and also pushes downwards upon the persons shoulders, using a downward force of 200 N. With the added downward pressure of 200 N acting upon the perkid, the total upward pressure must be 1000 N. The normal force supplies the upward force to assistance both the force of gravity and the used force acting upon the person. Its value is equal to 1000 N which is not the same as the pressure of gravity of the perkid.


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12. Which one(s) of the following pressure diagrams depict an object moving to the appropriate via a continuous speed? List all that use.

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Answer: AC

If an object is moving at a constant rate in a continuous rightward direction, then the acceleration is zero and the net pressure need to be zero. Choice B and also D show a rightward net force and also therefore a rightward acceleration, inregular through the explained motion.

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13. According to Newton's third legislation, eexceptionally pressure is accompanied by an equal and oppowebsite reactivity pressure. The factor that these forces execute not cancel each other is ____.

a. the action pressure acts for a longer time period

b. the two forces are not always in the very same direction

c. among the 2 pressures is higher than the other

d. the 2 pressures act upon different objects; just pressures on the same object can balance each other.

e. ... nonsense! They carry out cancel each various other. Objects accelerate bereason of the presence of a third force.

Answer: D

Action and also reaction forces always act upon the connecting objects for the same amount of time through the very same magnitude. So if object A pushes on object B, then object B concurrently pushes on object A through the same amount of pressure. The force on object B will be one of possibly many type of forces which will certainly govern its motion. But the reaction force is on object A and also cannot contribute to object B's activity because it is not acting upon object B. Action-reactivity forces deserve to NEVER cancel each other.

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14. As you sit in your chair and also examine your physics (presuming that you do), the pressure of gravity acts downward upon your body. The reactivity force to the force of the Planet pulling you downward is ___.

a. the force of the chair pushing you upward

b. the pressure of the floor pushing your chair upward

c. the force of the Earth pushing you upward

d. the force of air molecules pushing you upwards

e. the pressure of your body pulling the Earth upwards

f. ... nonsense! Gravity is a field pressure and also tright here is no such reactivity force.

Answer: E

The most common wrong answer is a - the force of the chair pushing you upward. As you sit in your chair, the chair is indeed pushing you upward but this is not the reaction force to the force of the Earth pulling you downward. The chair pushing you upward is the reactivity force to you sitting on it and also pushing the chair downward. To determine the action-reactivity force pairs if offered a statement of the develop object A pulls X-ward on object B, sindicate take the topic and the object in the sentence and switch their locations and also then readjust the direction to the opposite direction (so the reaction pressure is object B pulls object A in the opposite direction of X). So if the Earth pulls you downward, then the reaction force is you pull the Earth upward.

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15. A golf pro places a ball at remainder on the tee, lines up his shot, draws back his club, and lets one rip. Throughout the contact of the golf club via the golf ball, the pressure of the club on the sphere is ____ the force of the ball on the club and the acceleration of the club is ____ than the acceleration of the round.

a. greater than, greater than

b. greater than, equal to

c. higher than, much less than

d. much less than, less than

e. less than, equal to

f. much less than, better than

g. equal to, equal to

h. equal to, higher than

i. equal to, much less than

Answer: I

For eextremely activity, there is an equal and also opposite reactivity force. In this situation, the force on the club is equal to the force on the ball. The subsequent accelerations of the interacting objects will certainly be inversely dependent upon mass. The even more enormous club will have actually less acceleration than the less substantial sphere.

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Each one of Newton's Laws deserve to play a duty in any one certain situation. However, among the legislations is frequently most obviously dominant in governing the movement of a instance. Pick which of Newton's most governs the instances described below.

a. First Law (inertia)

b. Second Law (F = m•a)

c. Third Law (action-reaction)

16. A helicopter have to have actually two sets of knives in order to fly through stcapacity.

17. If you were in an elevator and also the cable damaged, jumping up just prior to the elevator hit the ground would not save you. Sorry.

18. You commonly jerk a record towel from a roll in order to tear it instead of pulling it smoothly.

19. A student desk alters the amount of force it puts on various other objects throughout a college day.

20. Heavy objects are not less complicated to move about in a horizontal fashion on the Moon than on the Earth.

21. The stronger, heavier team in a tug-of-war does not develop a larger stress and anxiety in the rope than the weaker, lighter team.

Answers: See answers and also explanations listed below.

16. C - As the helicopter knives spin and also press air in one direction, the air pushes the chisels in the opposite direction; the result is that the helicopter have the right to start to rotate about the axis of the blade. To counteract this rotation, a second set of blades is required.

17. A - An object moving downwards will continue to relocate downwards unless acted upon by an unbalanced pressure. If you make an initiative to supply such a pressure in an effort to suddenly change the direction of your movement, then you are developing a better velocity adjust than if you merely hit the ground and also quit. If this higher velocity change emerged suddenly (in the exact same amount of time as the protecting against of you and also the elevator), then you would certainly experience a greater acceleration, a greater net pressure, and also a greater ouch note than if you had actually merely hit the ground and also stopped.

18. A - The paper towel is at rest and also resists transforms in its at remainder state. So if you apply a sudden force to among the paper towel sheets, the good mass of the remainder of the roll will certainly withstand a readjust in its at rest state and the roll will certainly quickly break at the perforation.

19. C - As a student sits in the seat, they are using a downward force upon the seat. The reactivity pressure is that the seat applies an upward pressure upon the perboy. A weightier perkid will use even more downward force than a lighter person. Thus, the seat will certainly constantly be changing the amount of reactivity pressure throughout the day as students of different weight sit in it.

20. A - All objects have actually inertia or a propensity to resist changes in their state of movement. This inertia is dependent specifically upon mass and is subsequently not transformed by transforms in the gravitational environment. To move an object horizontally, one need to apply a force; this pressure will certainly be stood up to by the mass or inertia of the object. On the moon, the object offers the very same amount of inertia as on Earth; it is just as difficult (or easy) to move about.

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21. C - A rope encounters anxiety as soon as pulled on at both ends. The tension in the rope is anywhere the very same. If team A were to pull at the left end, then the left finish would pull back with the very same amount of pressure upon team A. This pressure is the same all over in the rope, consisting of at the finish where team B is pulling. Therefore team B is pulling earlier on the rope with the exact same pressure as team A. So if the forces are the exact same at each finish, then just how have the right to a team ever before win a tug-of-war. The means a more powerful team wins a tug-of-battle is via their legs. They press upon the ground with a higher force than the various other team. This force upon the ground outcomes in a pressure back upon the team in order for them to pull the rope and also the various other team backwards across the line.

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For the next several inquiries, take into consideration the velocity-time plot listed below for the activity of an item along a horizontal surface. The motion is split right into a number of time intervals, each labeled through a letter.

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22. During which time interval(s), if any kind of, are tright here no pressures acting upon the object? List all that apply.

23. During which time interval(s), if any, are the pressures acting upon the object balanced? List all that apply.

24. Throughout which time interval(s), if any type of, is there a net pressure acting upon the object? List all that use.

25. During which time interval(s), if any, is the net pressure acting upon the object directed toward the right? List all that use.

26. Throughout which time interval(s), if any, is the net pressure acting upon the object directed towards the left? List all that apply.

Answers: See answers and also explanations listed below.

22. None - If an object is on a surface, one have the right to be guaranteed of at least two pressures - gravity and also normal pressure.

23. BDFH - If the pressures are balanced, then an item is relocating via a continuous velocity. This is represented by a horizontal line on a velocity-time plot.

24. ACEG - If a things has actually a net pressure upon it, then it is accelerating. Acceleration is represented by a sloped line on a velocity-time plot.

25. AE - If the net pressure is directed to the right, then the acceleration is to the ideal (in the + direction). This is stood for by a line with a + slope (i.e., upward slope).

26. CG - If the net pressure is directed to the left, then the acceleration is to the left (in the - direction). This is stood for by a line via a - slope (i.e., downward slope).

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For the following a number of inquiries, consider the dot diagram below for the activity of a things along a horizontal surchallenge. The movement is divided into numerous time intervals, each labeled through a letter.

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27. Throughout which time interval(s), if any, are there no pressures acting upon the object? List all that apply.

28. Throughout which time interval(s), if any kind of, are the forces acting upon the object balanced? List all that use.

29. Throughout which time interval(s), if any kind of, is there a net force acting upon the object? List all that use.

30. During which time interval(s), if any type of, is the net force acting upon the object directed towards the right? List all that use.

31. Throughout which time interval(s), if any type of, is the net pressure acting upon the object directed toward the left? List all that apply.

Answers: See answers and explanations below.

27. None - If an item is on a surface, one have the right to be guaranteed of at least 2 forces - gravity and also normal pressure.

28. ACEGI - If the pressures are balanced, then an object is moving with a constant velocity or at remainder. This is represented by a section of a dot diagram wright here the dots are equally spaced acomponent (moving via a constant velocity) or not also spaced apart at all (at rest).

29. BDFH - If a things has a net pressure upon it, then it is speeding up. Acceleration is stood for by a area of a dot diagram in which the spacing between consecutive dots is either increasing or decreasing.

30. BF - If the net force is directed to the best, then the acceleration is to the right (in the + direction). This is represented by a dot diagram in which the dots are enhancing their separation distance as the object moves from left to best.

31. DH - If the net pressure is directed to the left, then the acceleration is to the left (in the - direction). This is stood for by a dot diagram in which the dots are decreasing their separation distance as the object moves from left to ideal.

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For the next a number of questions, think about the trajectory diagram displayed listed below for a projectile thrvery own at an angle to the horizontal. The vector arrows represent the horizontal and also vertical components of the projectile's velocity. Several points in the trajectory are labeled through a letter. Use the trajectory diagram to answer the following numerous concerns. (Consider air resistance to be negligible.)

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32. At which point(s), if any kind of, are tbelow no pressures acting upon the object? List all that use.

33. At which point(s), if any, are the forces acting upon the object balanced? List all that apply.

34. At which point(s), if any type of, is tbelow a net pressure acting upon the object? List all that use.

35. At which point(s), if any kind of, is the net force acting upon the object directed towards the right? List all that apply.

36. At which point(s), if any, is the net force acting upon the object directed upward? List all that apply.

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Answers: See answers and explanations below

32. None

33. None

34. ABCDEFG

35. None

36. None

This object is a projectile as can be watched by its consistent horizontal velocity and an altering vertical velocity (besides that, the problem states that this is a projectile). A projectile is a things upon which the just force is gravity. Gravity acts downward to acceleprice an item downward. This force is an unbalanced pressure or net pressure. It causes a vertical increasing object to sluggish down and a falling object to rate up.

The presence of a horizontal velocity does not demand also a horizontal pressure, just a balance of horizontal pressures. Having no forces horizontally would certainly reason the projectile to relocate at a continuous horizontal speed as soon as it is released. Similarly an upward force is not necessary on this projectile. When released, an upward velocity is imparted to it; this velocity is steadily diminished as the object is acted upon by the downward pressure of gravity. An upward pressure would certainly just be required for an item which is increasing as it rises upward.

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