Lesson 5: Chapter 5 Application of Laws of Force and Motion

Which best describes the velocity of the cannonball after it is fired? Pick all that apply. A. A vertical velocity that stays constant. B. A vertical velocity that changes so it is more downward. C. A vertical velocity that changes so it is more upward. D. A sideways velocity that stays constant. E. A sideways velocity that increases in size. F. A sideways velocity that gradually decreases.

- a vertical velocity that changes so it is more downward - a sideways velocity that stays constant

Which of the following diagrams best describes the forces on the package at this time? (take into account air friction and gravity)

- air friction up and to the right - gravity down

What are the forces on the tractor and the plow in the horizontal direction? Check all that apply. A. Gravity B. Electromagnetic force due to charged particles on the plow C. Friction backwards on the plow D. Friction forwards on the tractor E. There are no horizontal forces

- friction backwards on the plow - friction forwards on the tractor

The tractor is pulling the plow at a constant speed and in a straight line across the field. Now what are the forces on the tractor and the plow in the horizontal direction? Check all that apply. A. Gravity B. Electromagnetic force due to charged particles on the plow C. Friction forward D. Friction backward

- friction forward - friction backward

A farmer connects his tractor to a plow getting ready to plow his field. The engine is engaged, but the plow hasn't yet started to move. What are the forces on the tractor and the plow in the vertical direction? Check all that apply. A. Gravity B. Electromagnetic force due to charged particles on the plow C. Friction D. Contact force from the ground

- gravity - contact force from the ground

A 100 kg man and a 75 kg woman are having a tug-of-war. At this point, the two are at a standstill and nothing is moving. What are the forces on the man? (check all that apply) A. The force of the woman pulling on the man. B. The friction force of the ground pushing to the left on the man. C. The force of the man pushing on the ground. D. The normal force of the ground pushing up on the man. E. Gravity pulling down on the man. F. Gravity from the man pulling up on the earth.

- the force of the woman pulling on the man - the friction force of the ground pushing to the left on the man - the normal force of the ground pushing up on the man - gravity pulling down on the man

A man and a woman are having a tug-of-war. Now the man is winning and the woman has been accelerated forward. What are the forces on the man? (check all that apply) A. The force of the woman pulling on the man. B. The friction force of the ground pushing to the left on the man. C. The force of the man pushing on the ground. D. The normal force of the ground pushing up on the man. E. Gravity pulling down on the man. F. Gravity from the man pulling up on the earth.

- the force of the woman pulling on the man - the friction force of the ground pushing to the left on the man - the normal force of the ground pushing up on the man - gravity pulling down on the man

What are important questions to ask when analyzing a problem?

1. pick one object you want to find the forces on 2. answer the following question - is there a significant gravitational force? - are charges, currents, or magnets involved? - what is touching the object (contact force)? - are frictional forces significant? - air friction, water friction? - friction is significant when two things are being rubbed past each other 3. use Newton's laws to check and make sure you haven't forgotten any forces or added in forces that are not really there

The elevator can move sideways and vertically. He stands on a scale in an attempt to better understand the forces he experiences. As he enters the elevator and is at rest, the scale reads 165 pounds. What is the man's weight?

165

How many forces are on the woman? A. 1 B. 2 C. 3 D. 4

4

Which of Newton's Laws of Motion applies to this situation? A. Newton's 1st Law B. Newton's 2nd Law C. Newton's 3rd Law

Newton's 2nd law

Next tilt the cannon upward. If you fire the cannon at an angle does that change the answers to the questions above? Are your answers to the two questions the same when the cannon is fired upward? A. Both answers would be the same B. The answer to the acceleration question is the same, but the answer to the velocity question would change. C. The answer to the acceleration question would change, but the answer to the velocity question would stay the same. D. The answer to both questions would change.

both answers would be the same

What are the two significant forces acting on the man? A. Electromagnetic force due to the presence of a current and Gravity. B. Contact force and Gravity. C. Gravity and Air friction. D. Contact force and Electromagnetic force due to a net charge on the man. E. Contact force and Air friction.

contact force and gravity

The elevator continues upward at constant speed. The reading on the scale will be A. less than 165 pounds. B. equal 165 pounds. C. more than 165 pounds.

equal 165 pounds

The elevator abruptly stops and starts moving up vertically. While the elevator is speeding up, the reading on the scale will A. go down. B. stay the same. C. go up.

go up

The elevator then stops and starts moving down. The reading on the scale will be A. less than 165 pounds. B. equal to 165 pounds. C. more than 165 pounds.

less than 165 pounds

Are the forces on the woman balanced?

no

Are there charged objects, currents, or magnets present that could cause a significant electromagnetic force?

no

Is the man accelerating?

no

Is friction important? A. Yes, because in real life you can't just ignore friction. B. No, because it says to ignore it right in the problem.

no, because it says to ignore it right in the problem

What is the package touching? A. The ground B. A tree C. Nothing but air

nothing but air

Consider an airplane that is flying level at constant speed. The airplane drops a package. What happens to the package? Assume air friction can be ignored. What is the object to analyze? A. Airplane B. Bird C. Air Molecules D. Package

package

The elevator begins to move horizontally and soon is moving in uniform motion horizontally. The reading on the scale will A. go down. B. stay the same. C. go up.

stay the same

A bullet is fired horizontally from a high-powered rifle. At the same time, a second bullet is simply dropped from the same height as the bullet which was fired from the rifle. Neglecting air resistance, which statement is true about the acceleration of the first bullet after it leaves the gun compared to that of the second bullet as it falls? A. The acceleration of the first bullet is much less than the acceleration of the bullet that was dropped. B. The acceleration of the first bullet is a little less than the acceleration of the bullet that was dropped. C. The acceleration of the first bullet is the same as the acceleration of the bullet that was dropped. D. The acceleration of the first bullet is a little more than the acceleration of the bullet that was dropped. E. The acceleration of the first bullet is much more than the acceleration of the bullet that was dropped.

the acceleration of the first bullet is the same as the acceleration of the bullet that was dropped

What are the forces on the man that are balanced in the horizontal direction? A. The man's weight balances the upward contact force on the man. B. The man's weight balances the upward gravitational force on the earth. C. The contact force from the woman balances the frictional force from the ground. D. The frictional force from the ground balances the upward contact force on the man. E. The contact force from the woman balances the contact force from the man.

the contact force from the woman balances the frictional force from the ground

What are the forces on the man that are balanced in the vertical direction? A. The man's weight balances the upward contact force on the man. B. The man's weight balances the upward gravitational force on the earth. C. The contact force from the woman balances the frictional force from the ground. D. The frictional force from the ground balances the upward contact force on the man. E. The contact force from the woman balances the contact force from the man.

the man's weight balances the upward contact force on the man

What can you determine about the net force on the package? A. The net force is upward B. The net force is downward C. The net force is sideways D. The net force is zero

the net force is downward

If a parachute opened on the package, after a short while of falling, the upward air friction on the package would equal the downward gravitational force. How would you describe the motion of the package now? A. The package would continue to accelerate downward until it hit the ground. B. The package would start to move upward due to the increased air friction. C. The package would continue downward at a constant speed. D. The package would stop since the net force is zero.

the package would continue downward at a constant speed

How does the size of the force the woman exerts on the man compare to the size of the force that the man exerts on the woman. A. The two forces are equal in size. B. The force the woman exerts on the man is the larger of the two. C. The force the man exerts on the woman is the larger of the two.

the two forces are equal in size

If the 100 kg man and the 75 kg woman were standing on a perfectly frictionless surface and they started pulling on each other, what would happen? A. They would have the same acceleration because they would each have the same size unbalanced force acting on them. B. The man would accelerate more because he has more mass. C. The woman would accelerate more because she has less mass. D. Neither one of them would accelerate since there is no friction.

the woman would accelerate more because she has less mass

To use the animation, click "intro". You fire a projectile by clicking on the red cannon icon at the bottom of the page. To see the acceleration click the "total acceleration" button. Click the "slow" button so you can watch it more clearly, then fire away. Note: You are leaving the "air resistance" button off, so there is no air resistance. Which best describes the acceleration of the cannonball after it is fired? A. There is a constant downward acceleration. B. There is a sideways acceleration plus a downward acceleration.

there is a constant downward acceleration

An astronaut is floating outside a spacecraft in orbit around the Earth. There is no contact force between the astronaut and the spacecraft. What are the forces on the astronaut? A. None, she's weightless. B. There is an inertial force pushing her around the Earth. C. There is a gravitational force pulling her toward the Earth. D. There is an inertial force pulling her around the Earth and a gravitational force pulling her toward the Earth.

there is a gravitational force pulling her toward the earth

A raindrop, as it falls to the ground, reaches a speed known as terminal velocity where the speed of the raindrop is neither increasing nor decreasing. This motion of the raindrop at terminal velocity can be understood in terms of: A. one vertical force B. one horizontal force C. two vertical forces which balance D. two vertical forces which do not balance E. two horizontal forces which balance F. two horizontal forces which do not balance

two vertical forces which balance

In what direction is the force of air friction several seconds after the package has been dropped but before it reaches terminal velocity or hits the ground?

upward arrow slightly pointed to the right

As the elevator approaches the second floor, it begins to slow to a stop. Which choice properly describes her weight, contact force, and acceleration at this point? A. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is zero B. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is downward C. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is upward D. weight = 140 lbs downward, contact force = 130 lbs upward, acceleration is downward E. weight = 140 lbs downward, contact force = 130 lbs upward, acceleration is upward F. weight = 130 lbs downward, contact force = 120 lbs upward, acceleration is upward G. weight = 130 lbs downward, contact force = 120 lbs upward, acceleration is downward

weight = 130 lbs downward, contact force = 120 lbs upward, acceleration is downward

Now the elevator and the girl standing on the scale are mid-floor and are moving at a constant speed upward. Which choice properly describes her weight, contact force, and acceleration at this point? A. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is zero B. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is downward C. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is upward D. weight = 140 lbs downward, contact force = 130 lbs upward, acceleration is downward E. weight = 140 lbs downward, contact force = 130 lbs upward, acceleration is upward F. weight = 130 lbs downward, contact force = 140 lbs upward, acceleration is upward G. weight = 130 lbs downward, contact force = 140 lbs upward, acceleration is downward

weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is zero

A 130lb woman stands in an elevator on a scale as the elevator just begins to move upward from the first to second floor. Which choice could properly describe her weight, contact force, and acceleration at this instant? A. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is zero B. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is downward C. weight = 130 lbs downward, contact force = 130 lbs upward, acceleration is upward D. weight = 140 lbs downward, contact force = 130 lbs upward, acceleration is downward E. weight = 130 lbs downward, contact force = 140 lbs upward, acceleration is upward F. weight = 130 lbs downward, contact force = 140 lbs upward, acceleration is downward

weight = 130 lbs downward, contact force = 140 lbs upward, acceleration is upward

Are the forces on the man balanced?

yes

Are the horizontal forces balanced?

yes

Are the vertical forces balanced?

yes

Is there a significant gravitational force?

yes

Now let's look at the same situation of an airplane moving to the right dropping a package but this time take into account the effect of air friction. We already know that gravity is significant, there are no charged objects, currents, or magnets, and the package is not touching anything (besides air). Is friction important?

yes

Is the astronaut accelerating?

yes if an object isn't moving in a straight line then it is accelerating and the forces are not balanced

In a traffic accident an occupant of the front seat of a car can be thrown through the windshield if he is not wearing a seat belt. Which of the following is a correct explanation? A. The force of impact throws the occupants of the car forward. B. When you impact, force is backward, so there is an opposite and equal force forward on the occupants. C. You won't really go through the windshield, they only say that to get you to wear seatbelts. D. You are not thrown forward, you just keep on moving in the direction you were originally going until something, like the windshield, exerts a backwards force on you.

you are not thrown forward, you just keep on moving in the direction you were originally going until something, like the windshield, exerts a backwards force on you