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Newton'southward Laws Applications Review

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Part A: Drawing Free-Body Diagrams

1. Construct complimentary-body diagrams for the following physical situations.

a. A ball is dropped from balance from the peak of a edifice. Assume negligible air resistance. In the absence of Fair, the only force interim upon the brawl is gravity. Information technology is a projectile.	b. After being thrown, a football game is moving upwardly and rightwards towards the peak of its trajectory. Presume negligible air resistance. In the absence of Fair, the merely force acting upon the brawl is gravity. Information technology is a projectile. Notation that an upwards moving object does not need an upwards forcefulness. Only an upwardly accelerating object requires an upwardly force.	c. After reaching a terminal velocity, a falling skydiver then opens up the parachute. When the concluding velocity was reached, Fair = Fgrav. Then the parachute was opened, making Off-white even greater than before. This is represented by the larger arrow.
d. An air track glider is gliding to the right at constant velocity.  There is no rightwards strength. A rightwards force would only exist required if there is a rightwards acceleration. If the glider is gliding; there is no mention of it being pushed or pulled (Fapp) and if at that place is a constant velocity, there must be balanced forces.	e. A auto is skidding to a finish while travling to the correct.  There is no rightwards forcefulness. A rightwards force would but be required if there is a rightwards acceleration. If the car is skidding (wheels are locked), friction acts in a direction opposite its motion to slow it down.	f. A downward moving lift (held by a cable) slows downward. The cable supplies the tension force. Since the lift is moving downwardly and slowing down, there must exist more up forcefulness than the downwards gravity force.
g. A 25.0-N forcefulness is applied at a thirty-caste angle to a crate in guild to accelerate it rightward across a rough, horizontal surface. The applied strength is upwards and rightwards. Its upward component contributes to the upwards Fnorm to residue the force of gravity. (Note the relative size of Fnorm.)	h. A picture hangs summetrically by two wires oriented at angles to the vertical. The force exerted by a wire is a tension forcefulness. With 2 wires, at that place would be ii upwards-pulling tension forces. The down force is gravity.	i. A big crate slowly accelerated down a steep and rough inclined aeroplane. At that place are only three forces present. The Fpar and Fperp are only components of gravity; they are not dissever forces. The normal force is perpendicular to the surface (fatigued in blue).

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Part B: Conceptual Notions of Force and Motion

Limited your understanding of concepts of force, dispatch, and motion by answering the following questions.

2. Which of the post-obit are always truthful of an object that is at equilibrium? Include all that apply.

1. All the forces acting upon the object are equal.
2. The object is at residual.
3. The object is moving and moving with a abiding velocity.
4. The object has an acceleration of nil.
5. There is no change in the object'due south velocity.
6. The sum of all the forces is 0 N.
7. All the forces acting upon an object are balanced.

Answer: DEFG

These (DEFG) statements are always truthful. Statements ABC might be true but are not always true.

3. Which of the following are never true of an object that is at equilibrium? Include all that apply.

1. The object is accelerating.
2. The object is at rest.
3. The object is moving in a circumvolve at constant speed.
4. All the forces interim upon the object are equal.
5. The object is in costless-fall.
6. The object is falling and has reached its terminal velocity.
7. There is a net force acting upon the object.
8. The object is moving and moving with a constant velocity.

Reply: ACEG

An object that is at equilibrium tin can never be accelerating; its dispatch MUST exist 0 1000/s/southward. Thus, A is an answer; and considering an object in costless-fall (Due east) and an object moving in a circle (C) are also accelerating, they must be counted as answers besides. (NOTE: an object moving in a circle is irresolute its direction and equally such has an acceleration.) If there is a net force (G), so by definition the object is not at equilibrium. Choices B, D, F and H could be true of an object at equilibrium (though none of them are always truthful).

 

4. Large Bubba has a mass of 100 kg on the earth. What is Big Bubba's mass on the moon where the forcefulness of gravity is approximately 1/six-th that of World'due south? ________ Explain or show your work.

Respond: 100 kg

Mass is the corporeality of matter nowadays in the object and is independent of the weight of the object. The weight or force of gravity interim upon an object depends upon the mass and the dispatch of gravity (F_grav = m•g). Because grand is different on dissimilar planets and locations in the universe, the forcefulness of gravity or weight of an object will non always be the same. If Big Bubba goes to the moon, he will weigh less due to the decreased acceleration of gravity. Nevertheless, he will all the same look the same, still accept the aforementioned corporeality of matter, and still have a mass of 100 kg. KNOW the stardom between mass and weight.

5. Trivial Billie weight 360 North on World. What is Piddling Billie'due south mass on the moon where the force of gravity is approximately one/half-dozen-th that of Earth'south? ________ Explain or show your piece of work.

Reply: 37 kg (approx.)

The acceleration of gravity on the moon is 1/half-dozen-th the value of world's; this explains why the force of gravity is 1/6-thursday that of earth's. The strength of gravity ( F_grav ) on the moon is calculated using the equation F_grav = m•g where thou =ane.6 m/southward/s (on the moon). If Little Billie'due south weight on the moon is 1/6-th of 360 N, then Little Billie weighs sixty N on the moon. Inserting 60 N into the equation with 1.6 m/s/s as the value of m, Little Billie'due south mass can be calculated to be approximately 37 Northward. (Alternatively, just detect Billie's mass on earth from his weight of 360 Northward and then conclude that this mass value is not going to alter when he goes to the moon.)

6. TRUE or FALSE:

An object which is moving rightward has a rightward force interim upon information technology.

Answer: Imitation

A rightward acceleration would require a rightward net force. But if an object is moving rightward and slowing down (a leftwards acceleration), and so there is certainly not a rightward cyberspace force and peradventure not even a rightward force at all. For instance, if a motorcar is moving rightward and skidding to a stop (with wheels locked), so at that place is no rightward force upon the auto. The only horizontal force is a leftward strength of friction which serves to deadening the car down. (If you're gettingstuck on this question and ones like them, it might be time to read the folio titled "The Big Misconceptsion"; use the link beneath.)

7. How much cyberspace forcefulness is required to go on a v-kg object moving rightward with a abiding velocity of 2 m/southward? ________ Explicate or show your work.

Respond: 0 N

If the velocity is constant, so the dispatch is 0 yard/s/s and the internet force is zero. A cyberspace force is only required in order to accelerate an object. Yes, this ways that an object tin be moving to the right and NOT have a rightward's net strength. (If you're gettingstuck on this question and ones like them, it might be time to read the folio titled "The Big Misconceptsion"; use the link below.)

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8. True or False:

For an object resting upon a non-accelerating surface, the normal forcefulness is equal to the forcefulness of gravity.

Answer: Faux

In this instance, the normal strength could be equal to the strength of gravity. Just all that nosotros can conclusively know is that the all the vertical forces sum up to 0 N. If the object is upon an incline, then the normal forcefulness will not be equal to the strength of gravity. Or if there is another force with an upward or downwards component, and so the normal strength is not equal to the forcefulness of gravity.

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9. An object rests upon an inclined plane. If the bending of incline is increased, and then the normal forcefulness would _______.

a. increase

b. decrease

c. remain the same

Respond: B

The normal force is equal to the perpendicular component of the weight vector. So F_norm = F_perp = m•1000•cos(bending). If the incline bending is increased, the cos(angle) decreases towards 0; thus, the normal force decreases as well. Of course, the farthermost is when the angle is ninety degrees and there is no normal force.

10. Three pictures of equal weight (20 Due north) are hung by wires in three different orientations. In which orientation are the wires least likely to break? _______ Explain why.

Answer: threescore-degree angle to the horizontal

The tension in the wire volition accept the greatest impact upon its tendency to break. Every bit the wire becomes virtually vertically oriented, the horizontal component of the tension force is reduced and the tension becomes less. The moral of the story -- to back up the weight of a motion-picture show, one only needs to pull upwards, not leftwards and rightwards. Of course, the all-time arrangement would exist two wires pulling completely vertically.

eleven. A 50-Northward force is applied at an bending of 30 degrees northward of east. This would be the same as applying two forces at

1. 43 North, east and 7 N, north
2. 35 Northward, east and 15 N, north
3. 25 N, e and 25 N, north
4. 43 N, e and 25 N, due north

Answer: D

A 50-N forcefulness at 30 degrees would take 2 components - 43 Northward, east and 25 North, north. These two forces would exist equal to the l-Due north force at 30 degrees N of E. They are calculated as:

F_east = (l Due north)*cos(30 deg)

F_northward = (fifty Northward)*sin(xxx deg)

 

12. Which one(south) of the following force diagrams depict an object moving to the correct with constant speed? Write all possible answers (if whatever) in the blank: ________________

Explain your answer(southward) to this question.

Reply: Air-conditioning

Only A and C could have a constant speed. Both B and D would have an acceleration that is directed rightwards. Practice not confuse acceleration, motility, and strength. A rightwards dispatch requires that at that place be a rightwards internet force, On the other hand, a rightwards motility could have no net force, a leftward net force or a rightwards net force; it depends upon whether the object is slowing downward, speeding up or maintaining a constant speed. Simply A and C testify a balance of forces, so merely A and C are moving with constant speed. If you're gettingstuck on this question and ones like them, information technology might exist time to read the page titled "The Big Misconception"; use the link below.

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Source: https://www.physicsclassroom.com/reviews/Forces-in-2D/Forces-in-2D-Review-Answers-1

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