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Chapter 4 Review Questions

- Chapter 13 contains Review Questions Answers and Explanations.

- An object that is moving at a constant speed travels around a path.

- If an object is speeding up moving in the positive direction, slowing down moving in the positive direction, and slowing down moving in the negative direction, it's in section 5 of the velocity-time graph.

- A baseball is thrown.

- A rock is dropped off a cliff and hits the ground with a speed of 30 m/s.

- A stone is thrown from a bridge.

- A stone is thrown from a bridge.
- If air resistance is insignificant, you can find the stone's total speed when it enters the water.

- A stone is thrown with an initial speed of 5 m/s.

- The motion of a car on a straight track is the subject of this question.

- Consider a projectile moving in a straight line.

- A cannonball is shot with an initial speed of 50 m/s at a launch angle of 40deg away from the castle wall.
- The wall is 30 m high.

- A cannonball is fired with an initial speed of 40 m/s and a launch angle of 30o from a cliff that is 25 m tall.

- Summary graphs can be used to see the motion of an object.

- Once you learn how to translate from one graph to another, you can solve problems.

- Look at the axes first.
- One of the most common mistakes students make is thinking of a velocity-versus-time graph as if it were a position-versus-time graph.

- One box is one unit.

- Key points can be matched from one graph to the next.

- The Big Five equations can be used to describe the motion of an object.
- Look for what is given, determine what you're looking for, and use the equation that has those variables in it.

- It is important to separate the horizontal and vertical components of projectiles.

- Nature is happy with simplicity.

- The basis for dynamics can be found in three of the laws that were stated in The Principia.

- To understand the cause of motion, we need to look at dynamics.

- A push or pull is force.
- An apple can fall from a tree.
- Pull the door handle and it opens the door.
- You have to move a crate if you push on it.
- There is force required for these actions to happen.
- The Earth exerts a downward pull on it when an apple falls from a tree.
- The normal force is provided by the floor when you stand on it.
- The floor exerts a force against the crate when you slide it across it.

- Unless an unbalanced force acts on an object, the object's speed will not change: If the object is at rest, then it will stay at rest; if it is moving, then it will continue to move at a constant speed in a straight line.

- There are two identical boxes, one empty and one full.

- The box that's full has more mass because it contains more stuff.
- If a force produces a change in velocity for a 2 kilo object, then a 1 kilo object would experience the same change.
- inertia is a reflection of an object's mass and is a proxy for the extent of inertia inherent in an object.

- The forces are represented by their magnitude and direction.

- If object 1 exerts a force on object 2, object 2 exerts a force back on object 1 equal in strength but opposite in direction.

- The First Law says that an unbalanced force can't stop an object from moving.
- There is no net force required to keep a 5,000 kilogram object moving at a constant speed.

- There is a force that is opposite of the direction of motion that is slowing the car down.
- The net force on the car is zero because the gas supplies energy to the engine to spin the tires.

- 8 N is the weight of 2 kilograms (4 m/s2).

- An object feels two forces, one pulling to the left and the other pulling to the right.

- Adding and subtracting forces are possible.
- An 8 N force to the left added to a 20 N force to the right yields a net force of 12 N to the right.
- 3 m/s2 to the right is 12 N to the right.

- The object is experiencing zero net force if it is not increasing or decreasing in speed.

- There are three laws that will appear in later concepts.

- In simpler terms, let's sum up those three laws.

- Mass and weight are not the same thing and are often used interchangeably in everyday life.

- Mass is a measure of the amount of matter in an object.
- An object's mass does not change.

- Depending on the location, the weight changes.
- You weigh less on the Moon than on Earth.

- Mass is a proxy for inertia.

- Mass and weight are measured in newtons.

- A person is over 150 pounds.

- There is a book on a table.

- The table exerts force on the book.

- The downward pull of the Earth's gravity is felt by the book, as well as the upward force by the table.

- The net force on the book must be zero since the book is at rest.
- 20 N is the weight of 2 kilo(10 m/s2).

- The surface exerts a force on the object when it is in contact with it.

- The force that prevents objects from falling through the floor is the normal force.

- There is a book on a table.

- The table on the book has the normal force exerted on it.

- The downward pull of Earth's gravity is felt by the book, as well as the upward force by the table.

- The net force on the book must be zero since the book is at rest.

- The lowest level of understanding is found in the previous examples.
- Most of the physics is not easy to understand.
- There is more than one force acting on an object.
- If you follow the below strategy you can greatly increase your chance of success.

- To represent the object, draw a dot.
- To represent any forces acting on the object, draw arrows away from the dot.

- Anything touching the object exerts force.

- Ropes can only pull something if it is a rope.

- A surface can exert two forces if the object is a table, ramp, floor, or some other flat surface.

- The surface exerts force on itself.
- The normal force is always present if two things are in contact.

- The surface exerts a force on the object that is parallel to the surface and opposite to the direction of motion if there is kinetic friction present.

- There are things that can exert force without touching an object.
- The mystery of gravity pulls the Earth down.
- Electricity and magnetism exert their influences without being touched.

- You should draw that arrow longer than the smaller force's arrow if you know that one force is bigger than the other.

- Don't draw a force on it.
- There is no force of inertia.

- Define an appropriate coordinate system.

- Do the math.

- The following examples show how this strategy is used.

- Even on ramps, gravity points down.

- The force on the surface is not the same as the force on the ramps.

- The normal is relative to the surface, so don't put it opposite the direction of gravity.

- It is always parallel to the surface and tends to point in the opposite direction from motion.

- Draw a picture.
- Represent the object of interest as a heavy dot, and draw the forces that act on the object as arrows connected to the dot.

- 60 N is the number.

- The surface exerts a force on the object when it is in contact with it.

- Friction is caused by electrical interactions between atoms of which the object is composed and those of which the surface is composed.

- When the object is at rest, the bonds between the surfaces are weak.
- The bonds need to be broken before the object slides.
- The static force is higher than the kinetic force.

- The weak bonds cannot form fast enough when the object begins to slide.

- The strength of the force depends on two things: the nature of the surface and the strength of the normal force.
- The stronger the number is, the stronger the force.
- rubber-soled shoes and ice have the same coefficients of friction as rubber-soled shoes and a wooden floor.

- Weak forces that attempt to move an object can be counteracted by static friction.

- The coefficients of static friction between it and the surface it's on is not very high.
- The object won't move.
- The net force on an object is zero.
- If you want the object to slide, you have to overcome the maximum static friction force.

- A crate of mass is moving.
- The crate and the floor have the same coefficients.

- 200 N. is the weight of (20 kilo)(10 m/s2).

60 N is defined as (0.3)(200 N)

- 1.5 m/s2 is the amount of 30 N/ 20 kg.

- The coefficients of static friction are not very high.

- This example shows how static friction can change.

- In the diagram above, you should assume that the table is easy to use.
- The blocks should be released from rest.

- The object in the system is moving fast if the net force is not zero.
- The second law can be used to calculate the acceleration of objects.

- Again, draw a free-body diagram for each object.

- The tension in the cord was calculated in the previous example.

- An inclined plane is a ramp.
- If you look at the forces acting on a block that sits on a ramp using a standard coordinate system, it looks simple.
- The math has the potential to be difficult.

- A block slides down a plane that makes a 30 degree angle with the horizontal.

- A block slides down a plane with a horizontal angle.
- The acceleration of the block can be found if the coefficient of kinetic friction is less than 0.3.

- The first thing to do is draw a free-body diagram.

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