Chapter 4

One of the authors of this text has a weight of 500 N. What is her weight in pounds? (1 lb = 4.45 N) The weight in pounds is___kg

112.4kg

One of the authors of this text has a weight of 500 N. What is her mass in kilograms? (Use g = 9.81 m/s2) (You must provide an answer before moving to the next part.) The author's mass is___kg

51kg

Patricia has a weight of 137 lb. What is her mass in kilograms? (Use g = 9.81 m/s2) Patricia's mass is___kg

62.15kg

The belief that a force is necessary for motion to continue at constant velocity was advanced by

Aristotle

An upward force of 34.4 N is applied via a string to lift a ball with a mass of 2.3 kg. What is the net force acting upon the ball? (You must provide an answer before moving to the next part.) The net force acting upon the ball is___N

Fnet=34.4 N−22.54 N =11.86N

A 1.7-kg book rests on a table. A downward force of 14 N is exerted on the top of the book by a hand pushing down on the book. What is the magnitude of the upward (normal) force exerted by the table on the book? (Is the book accelerated?) (Round the final answer to four decimal places.) The magnitude of the upward force is______N, and the book is ____

F=16.7 N+14 N =30.7N not accelerated

An 5-kg block is acted upon by three horizontal forces A = 4 N, B = 16 N, and C = 8 N, as shown in the diagram. What is the net horizontal force acting on the block? (You must provide an answer before moving to the next part.) The net horizontal force acting on the block is___N

Fnet=4 N+16 N−8 N =12N

A 5-kg block being pushed across a table by a force P has an acceleration of 6 m/s2. What is the net force acting on the block? (You must provide an answer before moving to the next part.) The net force acting on the block is_____N

Fnet=5 kg×6 m/s2 =30N

A heavy ball with a mass of 7 kg is observed to accelerate at a rate of 9 m/s2. What is the magnitude of the net force acting on this ball? The magnitude of the net force acting on the ball is____N

Fnet=7 kg×9 m/s2 =63N

A 75-kg woman in an elevator is accelerating upward at a rate of 0.6 m/s2. What is the net force acting upon the woman? (You must provide an answer before moving to next part.) The net force acting upon the women is __N

Fnet=75 kg×0.6 m/s2 =45N

A 10-kg sled sliding freely on an icy surface experiences a 5-N frictional force exerted by the ice and an air-resistive force of 0.6 N. What is the net force acting on the sled? (You must provide an answer before moving to the next part.) The net force on the sled is___N

Fnet=−(5+0.6) N =(-5.6N)

The starship Enterprise locks onto an alien ship (whose mass is much greater than the Enterprise's mass) with its tractor beam (think of this as a futuristic rope) and starts to pull the alien ship toward it. Neither ship has its propulsion engines running. Which ship has greater acceleration towards the other?

The Enterprise

A 1.7-kg book rests on a table. A downward force of 14 N is exerted on the top of the book by a hand pushing down on the book. What is the net force on the book? Is it accelerating? (You must provide an answer before moving to the next part.) The net force on the book is____ , and the book is_____

The net force on the book is zero, and the book is not accelerating.

A shiny, spherical, metal alien jumps out of a perfectly good airplane and skydives for a few seconds. Its photographic friend snaps photos of the sphere with a special camera that also captures the forces on the object. Refer to the set of snapshots Q, J, Y, and L. Which snapshot depicts the forces just after the parachute has fully opened?

The snapshot in which the upward force is greater than the downward force is the correct answer

It is difficult to stop a car on an icy road surface. It is also difficult to accelerate a car on this same icy road. Which of the follow best explains why that is?

There is little to no friction between the the tires and the ground.

A 1.7-kg book rests on a table. A downward force of 14 N is exerted on the top of the book by a hand pushing down on the book. What is the magnitude of the gravitational force acting upon the book? (You must provide an answer before moving to the next part.) (Round the final answer to four decimal places.) The magnitude of the gravitational force acting upon the book is___N

W=1.7 kg×9.81 m/s2 =16.7N

An upward force of 34.4 N is applied via a string to lift a ball with a mass of 2.3 kg. What is the gravitational force acting on the ball? (You must provide an answer before moving to the next part.) The gravitational force acting on the ball is___N

W=2.3 kg×9.8 m/s2 =22.54N

At a given instant in time, a 30-kg rock is observed to be falling with an acceleration of 6.5 m/s2. What is the magnitude and direction of the gravitational force on the rock? (You must provide an answer before moving to the next part.) The magnitude of the gravitational force on the rock is ______N, and its direction is______

W=30 kg×9.8 m/s2 =294 N downward

At a given instant in time, an 8-kg rock that has been dropped from a high cliff experiences an upward force of air resistance of 12 N. What is the gravitational force on the rock? (Round the final answer to one decimal place.) The gravitational force on the rock is___N

W=8 kg×9.8 m/s =78.4N

What is the weight of a 90-kg mass? Use g = 9.81 m/s2.

W=90 kg×9.81 m/s2=882.9 N

Compared to its reading when at rest, a bathroom scale with a person standing on it in an elevator that is accelerating upward would indicate

a greater reading

You stand on a scale to measure your weight. The reaction to the force the Earth exerts on you is

the force you exert on the Earth.

Patricia has a weight of 137 lb. What is her weight in newtons? (1 lb = 4.45 N) (You must provide an answer before moving to the next part.) Patricia's weight is____N

609.65 N

At a given instant in time, an 8-kg rock that has been dropped from a high cliff experiences an upward force of air resistance of 12 N. What is the net force on the rock? (Note the directions of the two forces!) (You must provide an answer before moving to the next part.) (Round the final answer to one decimal place.) The net force on the rock is___N

78.4 N−12 N =66.4 N

At a given instant in time, a 30-kg rock is observed to be falling with an acceleration of 6.5 m/s2. What is the magnitude of the force of air resistance acting upon the rock at this instant? The magnitude of the force of air resistance is ____N, and its direction is____

F=195 N−30 kg×6.5 m/s2 =99N upwards

At a given instant in time, a 30-kg rock is observed to be falling with an acceleration of 6.5 m/s2. What is the magnitude and direction of the net force on the rock? (You must provide an answer before moving to the next part.) The magnitude of the net force is ____N, and its direction is______

F=30 kg×6.5 m/s2 =195N downward

A toy powered tractor pushes a book across a table to the right. Which of the following is the correct free-body diagram for the book?

Free-body diagram where the net force =0

A toy powered tractor pushes a book across a table to the right. Which of the following is the correct free-body diagram for the tractor?

Free-body diagram where the net force =0

A 75-kg woman in an elevator is accelerating upward at a rate of 0.6 m/s2. What is the gravitational force acting upon the woman? (You must provide an answer before moving to next part.) The gravitational force acting upon the women is −___N

Gravitational force=75 kg×9.8 m/s2 =-735N

A 75-kg woman in an elevator is accelerating upward at a rate of 0.6 m/s2. What is the normal force pushing upward on the woman's feet? (Note: A picture of the forces on her will help.) The normal force pushing upward on the woman's feet is___N

Total downward force=−735 N−45 N =-780N

You have three carts connected by strings, as shown in the diagram. Assume their masses M1 , M2 , M3 are different from one another. If the acceleration of M1 is called a1 , the acceleration of M2 is called a2 and the acceleration of M3 is called a3 which of the following correctly states the relative size of each masses acceleration?

a1 = a2 = a3

A 10-kg sled sliding freely on an icy surface experiences a 5-N frictional force exerted by the ice and an air-resistive force of 0.6 N. What is the acceleration of the sled? The acceleration of the sled is ___m/s2

a=-5.6 N/10 kg =-0.56 m/s2

An upward force of 34.4 N is applied via a string to lift a ball with a mass of 2.3 kg. What is the acceleration of the ball? The acceleration of the ball is___m/s2

a=11.86 N/2.3 kg =5.16 m/s2

At a given instant in time, an 8-kg rock that has been dropped from a high cliff experiences an upward force of air resistance of 12 N. What are the magnitude and direction of the acceleration of the rock? (Round the final answer to one decimal place.) The magnitude of the acceleration is ____ m/s2, and the direction is______

a=66.4 N/8 kg =8.3 m/s2 downwards

An 5-kg block is acted upon by three horizontal forces A = 4 N, B = 16 N, and C = 8 N, as shown in the diagram. What is the horizontal acceleration of the block? (Round the final answer to two decimal places.) The horizontal acceleration is___m/s2

a=Fnet/m =12 N/5 kg =2.4m/s2

Two block with the same mass are connected by a string and are pulled across a friction-less surface by a constant force, F , exerted by a string (see diagram). Which of the following statements is correct about what will happen to the boxes?

both boxes will accelerate

A 5-kg block being pushed across a table by a force P has an acceleration of 6 m/s2. If the magnitude of P is 38 N, what is the magnitude of the frictional force acting upon the block? The magnitude of the frictional force acting upon the block is____N

f=38N−(5 kg×6 m/s2) =8N

Two block with the same mass are connected by a string and are pulled across a friction-less surface by a constant force, F , exerted by a string (see diagram). The tension in the string connecting the boxes will be ____ the tension of the string exerting the force, F.

less than

What is the mass of a 765-N weight? Use g = 9.81 m/s2. (Round the final answer to four decimal places.) The mass of a 765-N weight is______kg

m=765 N/9.81 m/s2 =77.9817 kg

Compared to its reading when at rest, a bathroom scale with a person standing on it in an elevator on which the cable has just broken and the elevator is in free fall would indicate

no reading at all

A ball hangs from a string attached to the ceiling, as shown in the diagram. What is the direction of the net force acting on the ball?

none, the net force equals zero

Suppose that a bullet is fired from a rifle in outer space where there are no appreciable forces due to gravity or air resistance acting on the bullet. Which is the correct situation for the bullet after it is fired if it does not hit anything?

the bullet will remain at the same speed

Suppose that a skydiver wears a specially lubricated suit that reduces air resistance to a small constant force that does not increase as the diver's velocity increases. In this situation which of the following statements is correct?

the diver will no longer experience a terminal velocity

The tablecloth trick is where a tablecloth is rapidly pulled out from under some dinnerware without disturbing the dinnerware appreciably. The dinnerware does move a small amount though. Which of the following explanations is correct for this situation?

the force of friction from the moving tablecloth only acts for a short time

A sprinter accelerates at the beginning of a 100-meter race and then tries to maintain a maximum speed throughout the rest of the race. Which of the following forces is responsible for accelerating the sprinter at the start of the race?

the force of friction of the ground on the runner's shoes

A sprinter accelerates at the beginning of a 100-meter race and then tries to maintain a maximum speed throughout the rest of the race. Which of the following is correct once the sprinter reaches her maximum velocity assuming she is running in a straight line?

the net force on her equals zero

The acceleration of gravity on the Moon's surface is about 1/6 of that on the Earth's surface. An object on the Earth is to be taken to the Moon. We can state that, compared to the Earth,

the object's mass will be the same but the weight will be less on the Moon.

You are in an elevator on the top floor of a large building when the supporting cable breaks and you find yourself in a condition of apparent weightlessness as the elevator falls.

there is no normal force acting on you

A 10-pound sack of potatoes falls from an airplane. As the velocity of the falling sack increases, so does the air resistance on it. When the air resistance equals 10 pounds, the acceleration of the sack will be

zero