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PHYS 102 January 2020 Online, section Wicker (0005), Spring 2020

Module 4 - CH 4 HW (Homework)

INSTRUCTOR

Katharine Wicker Embry Riddle Aeronautical University, FL

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54.28/100 54.3%

SUN, FEB 9, 2020 6:59 PM HST

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When answering the homework problems be careful to represent the units properly and place a space between the numeric value and the unit (for example 5.0 m/s, not 5.0m/s). Your response will be marked wrong if you enter the wrong units in your answer. You may enter numeric values as all numbers or in scienti�c notation. For example if your answer is 36,000,000 you may enter all the numbers or to enter the answer in

scienti�c notation, you would convert 36,000,000 to 3.6x107 and enter 3.6e7 (NOTE the lower case e). Likewise, a numeric value of 0.00000037

would be 3 7e 7

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For this assignment, you submit answers by question parts. The number of submissions remaining for each question part only changes if you submit or change the answer.

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2/8/2020 Module 4 - CH 4 HW - PHYS 102 January 2020 Online, section Wicker (0005), Spring 2020 | WebAssign

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The water in the plumbing in a house is at a gauge pressure of 380,000 Pa. What force does this cause on the top of the tank

inside a water heater if the area of the top is 0.9 m2? (Ignore atmospheric pressure.) 342,000 N

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A viewing window on the side of a large tank at a public aquarium measures 41 in. by 46 in. The average gauge pressure from the water is 6 psi. What is the total outward force on the window? 11,316 lbs

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would be 3.7e-7 Acceptable units are: Those listed in previous chapter homework Force F = N or lb (if dealing with pressure in psi) Weight density = lb/ft^3 Weight = lb Pressure = psi or Pa in the MKS units NOTES: 1. When you enter your answer for an essay question, you will receive 10% of the points possible for the question to let you know you entered an answer. Your instructor will review your answer and adjust the points depending on the quality and completeness of your answers. 2. If you need help for other questions, use the Read It link that will take you to the portion of the text dealing with the question. 3. When entering answers with a value less that 1.0, enter the numeric value accurate to four decimal places (three signi�cant �gures).

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2/8/2020 Module 4 - CH 4 HW - PHYS 102 January 2020 Online, section Wicker (0005), Spring 2020 | WebAssign

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A small statue is recovered in an archaeological dig. Its weight is measured to be 59.0 lb and its volume 0.09 ft3.

(a) What is the statue's weight density?

(b) What substance is it, most likely? diamond

silver

juniper wood

iron

lead

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A certain part of an aircraft engine has a volume of 1.2 ft3.

(a) Find the weight of the piece when it is made of lead.

(b) If the same piece is made of aluminum, what is its weight? 201.6 lb Determine how much weight is saved by using aluminum instead of lead.

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The depth of the Pacific Ocean in the Mariana Trench is 36,198 ft. What is the gauge pressure at this depth?

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A storage tank 29 m high is filled with gasoline. (Assume the tank is open and exposed to the atmosphere at the top.)

(a) Find the gauge pressure at the bottom of the tank.

(b) Calculate the magnitude of the force produced by the fluid that acts on a square access hatch at the bottom of the tank that measures 0.6 m by 0.6 m.

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655.56 lb/ft

16,180.51 p

4. –/7.14 points My Notes Ask Your Teacher

2/8/2020 Module 4 - CH 4 HW - PHYS 102 January 2020 Online, section Wicker (0005), Spring 2020 | WebAssign

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A modern-day zeppelin holds 9,070 m3 of helium. Compute its maximum payload at sea level. (Assume the helium and air to be at 0°C and 1 atm.)

Problem Statement: A modern-day zeppelin holds 7,800 m3 of helium. Compute its maximum payload at sea level. (Assume the helium and air to be at 0°C and 1 atm.)

Step 1: Write down what you know in symbolic form: For this problem we are given the volume in cubic meters, therefore we will use the fact that the weight density of a substance can be represented as the mass density of the substance times the acceleration due to gravity: Dw = Dg (see page 146 in the

text).

Volume: V = 7800 m3

Mass Density of air: D(air) = 1.29 kg/m3

Mass Density of helium: D(helium) = 0.18 kg/m3

Step 2: Write down what you don't know in symbolic form: Weight of helium: W = ? Buoyant force: Fb = ?

Maximum payload or Net Force: Fnet = ?

Step 3: Find an equation that contains what you know and what you don't know: Weight of helium: W = D(helium) x g x V(of helium) Buoyant force: Fb = D(air) x g x V(air)

In this case V(of helium) = V(air) = V Net Force: Fnet = Fb - W

Step 4: Solve the equation for what you don't know: Net Force: Fnet = Fb - W = D(air) x g x V - D(helium) x g x V = [D(air) - D(helium)] x g xV

Step 5: Plug in (substitute) what you know and you will find out what you don't know:

Net Force: Fnet = Fb - W = [D(air) - D(helium)] x g x V = [1.29 kg/m3 - 0.18 kg/m3 ] x 9.8 m/s2 x 7,800 m3 = 1.11 kg/m3 x

9.8 m/s2 x 7,800 m3 = 84,848. 4 kg m/s2 (m3/m3) = 84,848.4 N

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A juniper-wood plank measuring 0.36 ft by 1 ft by 17 ft is totally submerged in water.

(a) What is its weight?

(b) What is the buoyant force acting on it?

(c) What is the size and the direction of the net force on it?

size

direction ---Select---

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10080.398

2/8/2020 Module 4 - CH 4 HW - PHYS 102 January 2020 Online, section Wicker (0005), Spring 2020 | WebAssign

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A rectangular block of ice with dimensions 2 m by 2 m by 0.2 m floats on water. A person weighing 980 N wants to stand on the ice. Would the ice sink below the surface of the water?

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The wing of an airplane has an average cross-sectional area of 13 m2 and experiences a lift force of 63,000 N. What is the average difference in the air pressure (in N/m^2)between the top and bottom of the wing?

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Yes

No

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Describe the four phases of matter. Compare their external, observable properties.

Solids: (Select all that apply.)

Liquids: (Select all that apply.)

Gases: (Select all that apply.)

Plasmas: (Select all that apply.)

Compare the nature of the forces between atoms or molecules (or both) in the solid, liquid, and gas phases.

Solids:

are generally good conductors of electricity and interact strongly with magnetic fields

can be compressed or squeezed into a smaller volume readily

flow readily, conforming to the shape of their container

have a well-defined boundary or surface

are rigid, and generally retain their shape unless distorted by a force

are generally good conductors of electricity and interact strongly with magnetic fields

can be compressed or squeezed into a smaller volume readily

flow readily, conforming to the shape of their container

have a well-defined boundary or surface

are rigid, and generally retain their shape unless distorted by a force

are generally good conductors of electricity and interact strongly with magnetic fields

can be compressed or squeezed into a smaller volume readily

flow readily, conforming to the shape of their container

have a well-defined boundary or surface

are rigid, and generally retain their shape unless distorted by a force

are generally good conductors of electricity and interact strongly with magnetic fields

can be compressed or squeezed into a smaller volume readily

flow readily, conforming to the shape of their container

have a well-defined boundary or surface

are rigid, and generally retain their shape unless distorted by a force

2/8/2020 Module 4 - CH 4 HW - PHYS 102 January 2020 Online, section Wicker (0005), Spring 2020 | WebAssign

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Liquids:

Gases:

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The attractive forces bind particles together, but not rigidly so; each atom or molecule can move about relative to the others but is always in contact with other atoms or molecules.

The attractive forces between particles are too weak to bind them together; atoms or molecules move about freely with high speed and are widely separated, only coming into contact when they collide.

The attractive forces are so strong that the atoms or molecules are rigidly bound to their neighbors and can only vibrate.

The attractive forces bind particles together, but not rigidly so; each atom or molecule can move about relative to the others but is always in contact with other atoms or molecules.

The attractive forces between particles are too weak to bind them together; atoms or molecules move about freely with high speed and are widely separated, only coming into contact when they collide.

The attractive forces are so strong that the atoms or molecules are rigidly bound to their neighbors and can only vibrate.

The attractive forces bind particles together, but not rigidly so; each atom or molecule can move about relative to the others but is always in contact with other atoms or molecules.

The attractive forces between particles are too weak to bind them together; atoms or molecules move about freely with high speed and are widely separated, only coming into contact when they collide.

The attractive forces are so strong that the atoms or molecules are rigidly bound to their neighbors and can only vibrate.

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Why is it that a person can lay still on a "bed" of nails (see the figure below) without suffering any serious injuries but would incur severe puncture wounds to his feet if he tried to stand barefoot on the same "bed"?

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A person lying still on a "bed" of nails has his weight distributed over a much larger area than if he were standing, and so the force (pressure ✕ unit area) on the person's skin is much greater when lying down. Because the upward force is

much greater when lying down, the net force (weight − force from nails) is closer to zero, and the nails do not puncture the skin.

A person lying still on a "bed" of nails takes up far more volume than a standing person, and so the buoyant force exerted by the air is much greater on a lying person than a standing person. Because the net force (weight − buoyant force) is much less, the pressure (force/unit area) is much less for a lying person, and the nails do not puncture the skin.

The weight of a person lying still on a "bed" of nails is much less than the weight of a standing person, and so the pressure (force/unit area) on the person's skin is much less when lying down. Because the pressure is much less when lying down, the nails do not puncture the skin.

A person lying still on a "bed" of nails has his weight distributed over a much larger area than if he were standing, and so the pressure (force/unit area) on the person's skin is much less when lying down. Because the pressure is much less when lying down, the nails do not puncture the skin.

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Would the weight density of water be different on the Moon than it is on Earth?

What about the mass density?

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The pressure in the air along the upper surface of an aircraft's wing (in flight) is lower than the pressure along the lower surface. Compare the speed of the air flowing over the wing to that of the air flowing under the wing.

Score: 0.718 out of 7.18

Comment:

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The air flowing over the wing travels at a higher speed which creates a lower pressure on top of the wing than underneath. This effect creates the lift required to elevate an aircraft off the ground and continue the flight. The wind below the wing is moving faster creating a higher pressure also.

Yes

No

The mass density would stay the same.

The mass density would not stay the same.

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