Physics Ch. 5

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question
When you push against a wall with your fingers, they bend. Identify the force or forces involved.
answer
You exert an action force and the wall exerts an equal and opposite reaction force.
question
A boxer can hit a heavy bag with great force. Why can't he hit a piece of tissue paper in midair with the same amount of force?
answer
The boxer can only hit the tissue paper with a force as large as the tissue paper can exert on the boxer, and the low-mass tissue can only exert a weak force.
question
How many forces are required for an interaction?
answer
Two forces, an action and a reaction, are needed for an interaction.
question
State Newton's third law of motion.
answer
For every action there is an equal and opposite reaction.
question
Consider hitting a baseball with a bat. If we call the force on the bat against the ball the action force, identify the reaction force.
answer
The reaction force is the force by the ball on the bat.
question
If the system of Figure 5.9 is only the orange, is there a net force on the system when the apple pulls?
answer
Yes, there is the action of the apple on the orange.
question
If the system is considered to be the apple and the orange together (Figure 5.10), is there a net force on the system when the apple pulls (ignoring friction with the floor)?
answer
The net force is zero because the action and reaction forces are equal and opposite.
question
To produce a net force on a system, must there be an externally applied net force?
answer
Yes, there must be an external net force on the system.
question
Consider the system of a single football. If you kick it, is there a net force to accelerate the system? If a friend kicks it at the same time with an equal and opposite force, is there a net force to accelerate the system?
answer
If you kick it, there is a net force; if both of you kick it, there is not.
question
Earth pulls down on you with a gravitational force that you call your weight. Do you pull up on Earth with the same amount of force?
answer
Yes, you pull up on Earth with the same force.
question
If the forces that act on a cannonball and the recoiling cannon from which it is fired are equal in magnitude, why do the cannonball and cannon have very different accelerations?
answer
Remember F = ma, and note that the cannon has a much greater mass than the cannon ball, so the cannon accelerates less for the same force.
question
Identify the force that propels a rocket.
answer
The rocket is propelled by the reaction force from the particles accelerated out the rear by an action force from the rocket.
question
How does a helicopter get its lifting force?
answer
The helicopter exerts downward forces on air; the reaction forces of the air on the helicopter are upward and called lift.
question
Can you physically touch a person without that person touching you with the same amount of force?
answer
When you touch a person, they must touch you with an equal and opposite force.
question
What is meant by the term vector resolution?
answer
A vector can be broken into two components at right angles that add together to make the original vector.
question
What happens to the magnitude of the normal vector on a block resting on an incline when the angle of the incline increases?
answer
The magnitude of the normal vector decreases.
question
What is the force of friction acting on a shoe at rest on an incline compared with the resultant of the vectors mg and N?
answer
It is equal and opposite.
question
How does the magnitude of the vertical component of velocity for a ball tossed at an upward angle change as the ball travels upward? How about the horizontal component of velocity when air resistance is negligible?
answer
The vertical component decreases in magnitude until it reaches the maximum height and then increases; the horizontal component is constant.
question
Fill in the blanks: Newton's first law is often called the law of ____; Newton's second law is the law of ____; and Newton's third law is the law of ____.
answer
Inertia, acceleration, action -reaction
question
Which of Newton's three laws focuses on interactions?
answer
Newton's third law
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