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Questions and Answers

Which force is defined as the force exerted by a surface supporting the weight of an object?

  • Frictional force
  • Normal force (correct)
  • Tension force
  • Applied force

What is the formula for calculating gravitational force (weight)?

  • $F_g = G \frac{m_1 m_2}{r^2}$
  • $F_g = ma$
  • $F_g = mg$ (correct)
  • $F_g = \mu F_N$

Which type of friction opposes the motion of objects already in motion?

  • Applied friction
  • Static friction
  • Kinetic friction (correct)
  • Normal friction

In a freebody diagram, what does the length of the arrow representing a force indicate?

<p>The magnitude of the force (C)</p> Signup and view all the answers

What does Newton's First Law of Motion, also known as the Law of Inertia, state?

<p>An object remains at rest or in uniform motion unless acted upon by a net external force (B)</p> Signup and view all the answers

A 10 kg object accelerates at a rate of 2 m/s. According to Newton's Second Law, what is the net force acting on the object?

<p>20 N (C)</p> Signup and view all the answers

When constructing a freebody diagram, what is the first step?

<p>Identify the object (D)</p> Signup and view all the answers

What is the purpose of a force diagram?

<p>To represent all forces acting on a single object (D)</p> Signup and view all the answers

According to Newton's Third Law, if you push against a wall, what is the reaction force?

<p>The wall pushing back on you with equal force (D)</p> Signup and view all the answers

A box with a weight of 50 N is resting on a flat surface. If the coefficient of static friction between the box and the surface is 0.4, what is the maximum static friction force that must be overcome to start moving the box?

<p>20 N (D)</p> Signup and view all the answers

Two objects with masses of 10 kg and 20 kg are separated by a distance of 1 meter. What is the gravitational force between them, given that (G = 6.67 imes 10^{-11} , ext{N}\cdot ext{m}^2/ ext{kg}^2) ?

<p>$1.334 \times 10^{-10} , \text{N}$ (A)</p> Signup and view all the answers

A car is traveling at a constant velocity. According to Newton's First Law, what can be said about the net force acting on the car?

<p>The net force is zero (D)</p> Signup and view all the answers

Consider a system where two blocks are connected by a rope over a pulley. Block A (5 kg) rests on a horizontal surface with a kinetic friction coefficient of 0.2 with the surface, and Block B (3 kg) hangs freely. What is the acceleration of the system?

<p>$2.45 , \text{m/s}^2$ (B)</p> Signup and view all the answers

A satellite orbits the Earth at a certain distance. If the distance between the satellite and the Earth were doubled, how would the gravitational force change?

<p>It would be quartered (A)</p> Signup and view all the answers

Imagine a scenario where a person is standing on a scale inside an elevator. Under what condition will the scale show a weight less than the person's actual weight?

<p>The elevator is accelerating downwards (C)</p> Signup and view all the answers

Which of the following forces always acts perpendicular to the surface of contact?

<p>Normal force (C)</p> Signup and view all the answers

What factor directly affects the magnitude of the gravitational force between two objects?

<p>The distance between the objects (D)</p> Signup and view all the answers

What is the net force acting on an object moving at a constant velocity in a straight line?

<p>Zero (B)</p> Signup and view all the answers

For an object resting on an inclined plane, which force component is used to calculate the frictional force?

<p>The component of weight perpendicular to the plane (A)</p> Signup and view all the answers

In a system where a box is being pulled across a floor at a constant speed, what can be said about the applied force ((F_a)) and the kinetic frictional force ((F_k))?

<p>$F_a = F_k$ (A)</p> Signup and view all the answers

If the distance between two objects is doubled, how does the gravitational force between them change?

<p>It is reduced to one-fourth (B)</p> Signup and view all the answers

What is the correct freebody diagram for a book sliding down an inclined plane with friction?

<p>Weight pointing downward, normal force pointing perpendicular to the plane, and friction pointing upwards along the plane. (C)</p> Signup and view all the answers

A stationary box experiences static friction from the floor. A force is exerted on the box, but it doesn't move. What happens to the static friction as the force is increased (but is still not enough to move the box)?

<p>It increases until it reaches a maximum value. (B)</p> Signup and view all the answers

Consider a scenario where two blocks are connected by a light string over a frictionless pulley. One block hangs vertically, and the other rests on a horizontal surface with friction. What condition must be met for the system to begin accelerating?

<p>The weight of the hanging block must be greater than the maximum static friction force acting on the block on the surface. (C)</p> Signup and view all the answers

A car accelerates from rest. Inside the car, a helium balloon is observed to move in a direction opposite to the car's acceleration. Which of Newton's Laws explains this phenomenon BEST?

<p>Newton's First Law (Law of Inertia) (C)</p> Signup and view all the answers

In a tug-of-war, two teams pull on a rope with equal and opposite forces. Despite this, the rope accelerates toward one of the teams. Which of the following could explain this?

<p>One team is exerting a greater force on the ground. (B)</p> Signup and view all the answers

A person is standing on a scale inside an elevator that is accelerating downwards. The scale reads 600 N. If the elevator's acceleration is 3 m/s, what is the person's approximate mass?

<p>91 kg (A)</p> Signup and view all the answers

Imagine a hypothetical scenario where the gravitational constant (G) suddenly doubled in value. Assuming all other physical parameters (masses, distances) remain constant, how would the gravitational force between two objects be affected?

<p>It would double. (C)</p> Signup and view all the answers

A block is placed on a ramp, and the angle of the ramp is slowly increased. At a certain angle, the block begins to slide. If the coefficient of static friction is (\mu_s) and the coefficient of kinetic friction is (\mu_k), what can be said about the relationship between these coefficients?

<p>(\mu_s &gt; \mu_k) (C)</p> Signup and view all the answers

A satellite is orbiting a planet in a perfectly circular orbit. Suddenly, a small propulsion system on the satellite fires, instantaneously increasing the satellite's speed in the direction of its orbit. Assuming this change in speed does not cause the satellite to escape the planet's gravity, what is the immediate effect on the satellite's trajectory?

<p>The satellite will enter an elliptical orbit. (B)</p> Signup and view all the answers

Which type of force is exerted by a rope or cable when it is pulled tight?

<p>Tension (D)</p> Signup and view all the answers

An object is at rest on a table. What is the relationship between the object's weight and the normal force exerted by the table?

<p>The normal force is equal to the object's weight. (C)</p> Signup and view all the answers

What is the SI unit of the gravitational constant G used in Newton's Law of Universal Gravitation?

<p>N · m²/kg² (C)</p> Signup and view all the answers

If an object is in motion, which type of friction primarily opposes its movement?

<p>Kinetic friction (A)</p> Signup and view all the answers

In a freebody diagram of a block sliding down an inclined plane, which of the following forces should be resolved into components parallel and perpendicular to the plane?

<p>Gravitational force (C)</p> Signup and view all the answers

According to Newton's First Law, what is the natural tendency of an object in motion?

<p>To continue moving at a constant velocity (D)</p> Signup and view all the answers

When constructing a freebody diagram, what does the point or simple shape represent?

<p>The object being analyzed (C)</p> Signup and view all the answers

A box is being pulled across a horizontal floor at a constant velocity. If the applied force is 75 N and the kinetic frictional force is also 75 N, what is the net force acting on the box?

<p>0 N (C)</p> Signup and view all the answers

What is the acceleration of a 10 kg object if a net force of 50 N is applied to it?

<p>5 m/s² (D)</p> Signup and view all the answers

Two cars collide head-on. According to Newton's Third Law, what can be said about the forces experienced by each car?

<p>Both cars exert equal forces on each other. (B)</p> Signup and view all the answers

A 2 kg block rests on a surface with a coefficient of static friction of 0.5. What minimum horizontal force is required to start the block moving?

<p>9.8 N (D)</p> Signup and view all the answers

An astronaut pushes off a spacecraft with a force of 100 N. If the spacecraft has a mass of 1000 kg, and the astronaut has a mass of 100 kg, what is the ratio of the spacecraft's acceleration to the astronaut's acceleration?

<p>10:1 (A)</p> Signup and view all the answers

Object A has a mass of m and Object B has a mass of 3m. They are separated by a distance r. What is the ratio of the gravitational force exerted by Object A on Object B to the gravitational force exerted by Object B on Object A?

<p>1:1 (C)</p> Signup and view all the answers

A car is able to accelerate at 3 m/s². Assuming that the engine force remains constant, but the car is now towing another car of EQUAL mass down a level road, what will its acceleration be?

<p>1.5 m/s² (C)</p> Signup and view all the answers

Flashcards

Gravitational Force (Weight)

The force with which the Earth pulls objects toward its center; equals mass times the acceleration due to gravity (9.8 m/s²).

Normal Force

The force exerted by a surface supporting an object, acting perpendicular to the surface.

Frictional Force

Force opposing the relative motion between two surfaces in contact; can be static (preventing motion) or kinetic (opposing motion).

Applied Force

An external force exerted on an object, like pushing or pulling.

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Tension

Force transmitted through a string, rope, or cable when pulled tight.

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Force Diagram

Represents all forces acting on a single object with arrows indicating direction and magnitude.

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FreeBody Diagram

Simplifies a force diagram by showing the object as a point with arrows representing external forces.

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Newton's First Law (Law of Inertia)

An object remains at rest or in uniform motion unless acted upon by an external force.

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Newton's Second Law (Law of Acceleration)

The acceleration of an object is directly proportional to the net force and inversely proportional to its mass (F = ma).

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Newton's Third Law (Action and Reaction)

For every action, there is an equal and opposite reaction.

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Newton's Law of Universal Gravitation

Any two objects with mass attract each other with a force proportional to the product of their masses and inversely proportional to the square of the distance between them.

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Static Friction

Force that prevents an object from starting to move.

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Kinetic Friction

Force that opposes the motion of moving objects.

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Force Diagram Representation

Tool showing forces as arrows, indicating direction and magnitude, on a single object.

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Resultant Force

The sum of all forces acting on an object.

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Equilibrium

Condition where the sum of forces in each direction equals zero, resulting in no acceleration.

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Force Components on Inclined Planes

Breaking forces into components parallel and perpendicular to the plane.

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Tension in Cables Analysis

Using freebody diagrams to determine the tension in systems involving pulleys or suspended objects.

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Inertia

Tendency of objects to resist changes in their state of motion.

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Gravitational Constant (G)

The constant in the Law of Universal Gravitation.

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What is Applied Force?

The force when an object is pushed or pulled.

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What is Tension?

The force transmitted through a rope or cable.

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What is a Force Diagram?

A diagram showing forces acting on an object.

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What is a FreeBody Diagram?

Diagram simplifying forces by representing the object as a point.

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What is an Equilibrium Problem?

Determining forces when the object isn't accelerating.

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Study Notes

Introduction to Newton's Laws of Motion

  • Crucial to understanding the dynamics of objects under the influence of forces in classical mechanics.
  • Forces are interactions that change the motion of objects.

Types of Forces

  • Gravitational force (weight).
  • Normal force.
  • Frictional force (static and kinetic).
  • Applied force (push or pull).
  • Tension.

Gravitational Force (Weight)

  • Earth pulls objects towards its center with this force.
  • (F_g = mg), where (F_g) is weight, (m) is mass, and (g) is the acceleration due to gravity (9.8 m/s² on Earth).
  • A rock with a mass of 5 kg has a gravitational force of 49 N ((F_g = 5 , \text{kg} \times 9.8 , \text{m/s}^2 = 49 , \text{N})).

Normal Force

  • A surface exerts this force to support the weight of an object resting on it.
  • Acts perpendicular to the surface.
  • Often balances the weight of an object on a flat surface.
  • A book weighing 10 N on a table experiences an equal upward normal force of 10 N from the table.

Frictional Force

  • Opposes the relative motion between two surfaces in contact.
  • Types: static friction (prevents motion from starting) and kinetic friction (acts against objects in motion).
  • Calculated as (F_f = \mu F_N), where (\mu) is the coefficient of friction, and (F_N) is the normal force.
  • A sled on snow with a coefficient of kinetic friction of 0.2 and a normal force of 100 N has a frictional force of 20 N ((F_f = 0.2 \times 100 , \text{N} = 20 , \text{N})).

Applied Force and Tension

  • External force exerted on an object, such as pushing or pulling.
  • Tension is transmitted through strings, ropes, or cables when pulled tight.
  • An applied force of 50 N is exerted when pulling a box with a force of 50 N.
  • The tension in a rope attached to the box equates the applied force, assuming no other forces act on the box.

Force Diagrams and FreeBody Diagrams

  • Essential for understanding forces acting on an object.

Force Diagrams

  • Represents all forces acting on a single object.
  • Each force is shown as an arrow indicating direction, with length representing magnitude.

FreeBody Diagrams

  • Simplifies force diagrams by representing the object as a point or simple shape.
  • Arrows represent all external forces acting on it.
  • A block on an inclined plane's freebody diagram includes gravitational force downward, normal force perpendicular to the plane, frictional force opposing motion, and any applied forces or tension.

Steps to Construct Force Diagrams

  • Identify the Object to analyze.
  • List All Forces, including gravitational, normal, frictional, and applied forces.
  • Draw the Diagram, representing the object and drawing arrows for each force, ensuring accurate directions and lengths.
  • Label the Forces clearly (e.g., (F_g), (F_N), (F_f)).
  • Calculate the Resultant Force (net force) by adding up all the forces, if needed.

Application in Problem Solving

  • Equilibrium Problems: If an object isn't accelerating, the sum of the forces in each direction equals zero.
  • Motion on Inclined Planes: Freebody diagrams help break forces into components parallel and perpendicular to the plane.
  • Tension in Cables: Freebody diagrams help determine the tension in systems involving pulleys or suspended objects.

Newton's First Law: The Law of Inertia

  • An object remains at rest or in uniform motion unless acted upon by an external force.
  • Passengers are thrown forward when a car suddenly stops due to inertia, continuing to move until acted upon by the seatbelt.

Newton's Second Law: The Law of Acceleration

  • The acceleration of an object is directly proportional to the net force acting on it and inversely proportional to its mass: (F = ma).
  • If a force of 100 N is applied to a 20 kg object, the acceleration is 5 m/s² ((a = \frac{100 , \text{N}}{20 , \text{kg}} = 5 , \text{m/s}^2)).

Newton's Third Law: Action and Reaction

  • For every action, there is an equal and opposite reaction.
  • Pushing a boat backward when jumping off is the action, and the boat pushing you forward is the reaction.

Newton's Law of Universal Gravitation

  • Any two objects with mass attract each other with a force: (F = G \frac{m_1 m_2}{r^2}).
  • (G = 6.67 \times 10^{11} , \text{N}\cdot\text{m}^2/\text{kg}^2), (m_1) and (m_2) are the masses, and (r) is the distance between their centers.
  • The gravitational force between two masses of 50 kg separated by 2 meters is (4.17 \times 10^{9} , \text{N}) ((F = 6.67 \times 10^{11} \times \frac{50 \times 50}{2^2} = 4.17 \times 10^{9} , \text{N})).

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