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Assignment 2: Newton's Laws of Motion

Due: 2:00am on Saturday, September 11, 2010

Note: To understand how points are awarded, read your instructor's Grading Policy.

[Switch to Standard Assignment View]

Pulling Three Blocks

Three identical blocks connected by ideal strings are being pulled along a horizontal frictionless surface

by a horizontal force . The magnitude of the

tension in the string between blocks B and C is

= 3.00 . Assume that each block has mass

= 0.400 .

Part A

What is the magnitude of the force?

Hint A.1 Find the acceleration of block B

Hint A.2 Find the acceleration of all three blocks

Express your answer numerically in newtons.

ANSWER:

= 4.50

Part B

What is the tension in the string between block A and block B?

Hint B.1 How to approach the question

Express your answer numerically in newtons

ANSWER:

= 1.50

Page 2

=

Correct

A woman rides on a Ferris wheel of radius 16 that maintains the same speed throughout its motion.

To better understand physics, she takes along a digital bathroom scale (with memory) and sits on it.

When she gets off the ride, she uploads the scale readings to a computer and creates a graph of scale

reading versus time. Note that the graph has a

minimum value of 510 and a maximum value

of 666 .

Part A

What is the woman's mass?

Hint A.1

Hint not displayed

Hint A.2

Hint not displayed

Hint A.3

Hint not displayed

Hint A.4

Hint not displayed

ANSWER:

=

Correct

A window washer of mass is sitting on a platform suspended by a system of cables and pulleys as

shown . He is pulling on the cable with a force of

magnitude . The cables and pulleys are ideal

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using high-performance parachutes; these offer the sky divers more maneuverability in the air but

increase the terminal speed up to 4 meters per second (10 miles per hour).

Block on an Incline Adjacent to a Wall

A wedge with an inclination of angle rests next to a wall. A block of mass is sliding down the plane,

as shown. There is no friction between the wedge and the block or between the wedge and the

horizontal surface.

Part A

Find the magnitude, , of the sum of all forces acting on the block.

Hint A.1 Direction of the net force on the block

Hint A.2 Determine the forces acting on the block

Hint A.3 Find the magnitude of the force acting along the direction of motion

Express in terms of and , along with any necessary constants.

ANSWER:

=

Part B

Find the magnitude, , of the force that the wall exerts on the wedge.

Hint B.1 The force between the wall and the wedge

Hint B.2 Find the normal force between the block and the wedge

Page 7

Hint not displayed

Hint B.3

Hint not displayed

ANSWER:

=

Correct

Your answer to Part B could be expressed as either or . In either

form, we see that as gets very small or as approaches 90 degrees ( radians), the contact

force between the wall and the wedge goes to zero. This is what we should expect; in the first

limit ( small), the block is accelerating very slowly, and all horizontal forces are small. In the

second limit ( about 90 degrees), the block simply falls vertically and exerts no horizontal force

on the wedge.

Below are birds-eye views of six identical toy cars moving to the right at 2 . Various forces act on the

cars with magnitudes and directions indicated below. All forces act in the horizontal plane and are either

parallel or at 45 or 90 degrees to the car's motion.

Part A

Rank these cars on the basis of their speed a short time after the forces are applied.

Hint A.1

Hint not displayed

Hint A.2

Hint not displayed

ANSWER:

View

Correct

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workers who hung the chandelier couldn't attach

the cables to the ceiling directly above the

chandelier. Instead, they attached the cables to

the ceiling near the walls. Cable 1 has tension

and makes an angle of with the ceiling.

Cable 2 has tension and makes an angle of

with the ceiling.

Part A

Find an expression for , the tension in cable 1, that does not depend on .

Hint A.1 Find the sum of forces in the direction

Hint A.2 Find the sum of forces in the direction

Hint A.3 Putting it all together

Express your answer in terms of some or all of the variables , , and , as well as the

magnitude of the acceleration due to gravity .

ANSWER:

=

At the Test Track

You want to test the grip of the tires on your new race car. You decide to take the race car to a small

test track to experimentally determine the coefficient of friction. The racetrack consists of a flat, circular

road with a radius of 45 . The applet shows the result of driving the car around the track at various

speeds.

Part A

What is , the coefficient of static friction between the tires and the track?

Hint A.1 How to approach the problem

Hint A.2 Use the applet to find the speed

Hint A.3 Find an expression for

Page 12

Find an expression for

Hint not displayed

Express your answer to two significant figures.

0.91

Correct

Score Summary:

Assignment 2: Newton's Laws of Motion

Due: 2:00am on Saturday, September 11, 2010

Note: To understand how points are awarded, read your instructor's Grading Policy.

[Switch to Standard Assignment View]

Pulling Three Blocks

Three identical blocks connected by ideal strings are being pulled along a horizontal frictionless surface

by a horizontal force . The magnitude of the

tension in the string between blocks B and C is

= 3.00 . Assume that each block has mass

= 0.400 .

Part A

What is the magnitude of the force?

Hint A.1 Find the acceleration of block B

Hint A.2 Find the acceleration of all three blocks

Express your answer numerically in newtons.

ANSWER:

= 4.50

Part B

What is the tension in the string between block A and block B?

Hint B.1 How to approach the question

Express your answer numerically in newtons

ANSWER:

= 1.50

Page 2

=

Correct

A woman rides on a Ferris wheel of radius 16 that maintains the same speed throughout its motion.

To better understand physics, she takes along a digital bathroom scale (with memory) and sits on it.

When she gets off the ride, she uploads the scale readings to a computer and creates a graph of scale

reading versus time. Note that the graph has a

minimum value of 510 and a maximum value

of 666 .

Part A

What is the woman's mass?

Hint A.1

Hint not displayed

Hint A.2

Hint not displayed

Hint A.3

Hint not displayed

Hint A.4

Hint not displayed

ANSWER:

=

Correct

A window washer of mass is sitting on a platform suspended by a system of cables and pulleys as

shown . He is pulling on the cable with a force of

magnitude . The cables and pulleys are ideal

Page 6

using high-performance parachutes; these offer the sky divers more maneuverability in the air but

increase the terminal speed up to 4 meters per second (10 miles per hour).

Block on an Incline Adjacent to a Wall

A wedge with an inclination of angle rests next to a wall. A block of mass is sliding down the plane,

as shown. There is no friction between the wedge and the block or between the wedge and the

horizontal surface.

Part A

Find the magnitude, , of the sum of all forces acting on the block.

Hint A.1 Direction of the net force on the block

Hint A.2 Determine the forces acting on the block

Hint A.3 Find the magnitude of the force acting along the direction of motion

Express in terms of and , along with any necessary constants.

ANSWER:

=

Part B

Find the magnitude, , of the force that the wall exerts on the wedge.

Hint B.1 The force between the wall and the wedge

Hint B.2 Find the normal force between the block and the wedge

Page 7

Hint not displayed

Hint B.3

Hint not displayed

ANSWER:

=

Correct

Your answer to Part B could be expressed as either or . In either

form, we see that as gets very small or as approaches 90 degrees ( radians), the contact

force between the wall and the wedge goes to zero. This is what we should expect; in the first

limit ( small), the block is accelerating very slowly, and all horizontal forces are small. In the

second limit ( about 90 degrees), the block simply falls vertically and exerts no horizontal force

on the wedge.

Below are birds-eye views of six identical toy cars moving to the right at 2 . Various forces act on the

cars with magnitudes and directions indicated below. All forces act in the horizontal plane and are either

parallel or at 45 or 90 degrees to the car's motion.

Part A

Rank these cars on the basis of their speed a short time after the forces are applied.

Hint A.1

Hint not displayed

Hint A.2

Hint not displayed

ANSWER:

View

Correct

Page 11

workers who hung the chandelier couldn't attach

the cables to the ceiling directly above the

chandelier. Instead, they attached the cables to

the ceiling near the walls. Cable 1 has tension

and makes an angle of with the ceiling.

Cable 2 has tension and makes an angle of

with the ceiling.

Part A

Find an expression for , the tension in cable 1, that does not depend on .

Hint A.1 Find the sum of forces in the direction

Hint A.2 Find the sum of forces in the direction

Hint A.3 Putting it all together

Express your answer in terms of some or all of the variables , , and , as well as the

magnitude of the acceleration due to gravity .

ANSWER:

=

At the Test Track

You want to test the grip of the tires on your new race car. You decide to take the race car to a small

test track to experimentally determine the coefficient of friction. The racetrack consists of a flat, circular

road with a radius of 45 . The applet shows the result of driving the car around the track at various

speeds.

Part A

What is , the coefficient of static friction between the tires and the track?

Hint A.1 How to approach the problem

Hint A.2 Use the applet to find the speed

Hint A.3 Find an expression for

Page 12

Find an expression for

Hint not displayed

Express your answer to two significant figures.

0.91

Correct

Score Summary: