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engineering
introduction mechanical engineering
An Introduction To Mechanical Engineering 3rd Edition Jonathan Wickert, Kemper Lewis - Solutions
Neglecting the presence of friction, air drag, and other inefficiencies, how much gasoline is consumed when a 1300-kg automobile accelerates from rest to 80 km/h? Express your answer in the units of mL. The density of gasoline is listed in Table 6.1.Table 6.1 Density, p Viscosity, u Fluid kg/m?
Wind turbines convert the kinetic energy of wind to mechanical or electrical power. The mass of air that hits a wind turbine each second is given by:where the density of air is 1.23 kg/m3 and the area is the area swept by the turbine rotor blades. This mass flow rate can be used to calculate the
As part of a packing and distribution system, boxes are dropped onto a spring and pushed onto a conveyor belt. The boxes are originally at a height h above the uncompressed spring [Figure P7.20(a)]. Once dropped, the box of mass m compresses the spring a distance ΔL [Figure P7.20(b)]. If all the
A small hydroelectric power plant operates with 500 gal of water passing through the system each second. The water falls through a vertical distance of 150 ft from a reservoir to the turbines. Calculate the power output, and express it in the units of both hp and kW. The density of water is listed
A 2500-lb automobile comes to a complete stop from 65 mph. If 60% of the braking capacity is provided by the front disk brake rotors, determine their temperature rise. Each of the two cast-iron rotors weighs 15 lb and has a specific heat of 0.14 Btu/(lbm ∙ °F).
A brick wall 3 m high, 7.5 m wide, and 200 mm thick has a thermal conductivity of 0.7 W/(m ∙ C°). The temperature on the inner face is 25°C, and the temperature on the outer face is 0°C. How much heat is lost per day through the wall?
A welding rod with k = 30 (Btu/h)/(ft ∙ 8F) is 20 cm long and has a diameter of 4 mm. The two ends of the rod are held at 500°C and 50°C.(a) In the units of Btu and J, how much heat flows along the rod each second?(b) What is the temperature of the welding rod at its midpoint?
A hollow square box is made from 1-ft2 sheets of a prototype insulating material that is 1 in. thick. Engineers are performing a test to measure the new material’s thermal conductivity. A 100-W electrical heater is placed inside the box. Over time, thermocouples attached to the box show that the
Give two examples each of engineering applications where heat would be transferred primarily through conduction, convection, and radiation.
A 5.0-kg steel gear is heated to 150°C and then placed into a 0.5-gal container of water at 10°C. What is the final temperature of the metal and water?
The interior contents and materials of a small building weigh 25 tons, and together they have an average specific heat of 0.25 Btu/(lbm ∙ °F). Neglecting any inefficiency in the furnace, what amount of natural gas must be burned to raise the building’s temperature from freezing to 70°F?
During processing in a steel mill, a 750-lb steel casting at 800°F is quenched by plunging it into a 500-gal oil bath, which is initially at a temperature of 100°F. After the casting cools and the oil bath warms, what is the final temperature of the two? The weight per unit volume of the oil is
The heating value of agricultural residue biomass (e.g., crop residues, animal manure and bedding, and organic material from food production), can range from 4300 to 7300 Btu/lbm. How much heat is released when 500 kg of biomass is burned?
Suppose that the truck in Problem P7.8 was going up a hill with a grade of 2%. How much additional power must the engine produce to climb the hill, neglecting various frictional effects?Data from Problem P7.8A light truck weighs 3100 lb and is rated at 30 miles per gallon for 60-mph highway driving
For the two automobiles of Problem P6.31 in Chapter 6, how much power must the engines produce just to overcome air drag at 60 mph?Problem P6.31(a) A luxury sports car has a frontal area of 22.4 ft2 and a 0.29 coefficient of drag at 60 mph. What is the drag force on the vehicle at this speed?(b) A
A baseball catcher stops a 98-mph fastball over a distance of 0.1 m. What is the force necessary to stop the 0.14-kg fastball?
A sprinter runs using a force of 200 N and a power output of 600 W. Calculate how many minutes it takes for the runner to run 1 km.
In the movie Back to the Future, Doc Brown and the young Marty McFly need 1.21 GW of power for their time machine.(a) Convert that power requirement to horsepower.(b) If a stock DeLorean sports car produces 145 hp, how many times more power does the time machine need?
A lawn mower engine is started by pulling a cord wrapped around a hub of radius 6.0 cm. If a constant tension of 80 N is maintained in the cord and the hub makes three revolutions before the motor starts, how much work is done?
A remote-controlled toy car weighs 3 lb and moves at 15 ft/s. What is its kinetic energy?
Beginning from their definitions, determine the conversion factor between ft ∙ lb and kW ∙ h in Table 7.1.Table 7.1 ft- Ib Btu kW -h 1 1.356 1.285 x 10-3 3.766 x 10-7 0.7376 1 9.478 x 10-4 2.778 x 10-7 778.2 1055 1 2.930 x 10-4 2.655 x 10 3.600 x 10° 3413 1
Water flows through a circular pipe having a constriction in diameter from 1 in. to 0.5 in. The velocity of the water just upstream of the constriction is 4 ft/s. By using the result of Problem P6.35, determine:(a) The velocity of the water downstream from it.(b) The pressure drop across the
A device called a venturi flowmeter can be used to determine the velocity of a flowing fluid by measuring the change in its pressure between two points (Figure P6.35, see on page 290). Water flows through a pipe, and, at the constriction, the cross-sectional area of the pipe reduces from A1 to the
(a) Use the principle of dimensional consistency to show that when Bernoulli’s equation is written in the formeach term has the dimension of pressure.(b) When the equation is written alternatively asshow that each term has the dimension of length. 1. p+ zou + pgb constant
Submarines dive by opening vents that allow air to escape from ballast tanks and water to flow in and fill them. In addition, diving planes located at the bow are angled downward to help push the boat below the surface. Calculate the diving force produced by a 20-ft2 hydroplane having a lift
A certain parachute has a drag coefficient of CD = 1.5. If the parachute and skydiver together weigh 225 lb, what should the frontal area of the parachute be so that the skydiver’s terminal velocity is 15 mph when approaching the ground? Is it reasonable to neglect the buoyant force that is
(a) A luxury sports car has a frontal area of 22.4 ft2 and a 0.29 coefficient of drag at 60 mph. What is the drag force on the vehicle at this speed?(b) A sport-utility vehicle has CD = 0.45 at 60 mph and a slightly larger frontal area of 29.1 ft2. What is the drag force in this case?
Place Equation (6.16) into the form of Equation (6.14) and show that the coefficient of drag for small Reynolds numbers is given by Equation (6.15).Equation 6.14Equation 6.15Equation 6.16 FD = PAVCD
A submarine releases a spherical flotation buoy containing a radio beacon. The buoy has a diameter of 1 ft and weighs 22 lb. The coefficient of drag for the submerged buoy is CD = 0.45. At what steady speed will the buoy rise to the surface?
A low-altitude meteorological research balloon, temperature sensor, and radio transmitter together weigh 2.5 lb. When inflated with helium, the balloon is spherical with a diameter of 4 ft. The volume of the transmitter can be neglected when compared to the balloon’s size. The balloon is released
A 14-mm-diameter sphere is dropped into a beaker of SAE 30 oil. Over a portion of its downward motion, the sphere is measured to fall at 2 m/s. In the units of newtons, what is the drag force acting on the test sphere?
A 175-lb skydiver reaches a terminal velocity of 150 mph during free fall. If the frontal area of the diver is 8 ft2, what are:(a) The magnitude of the drag force acting on the skydiver?(b) The drag coefficient?
(a) A 1.5-mm-diameter steel sphere (7830 kg/m3) is dropped into a tank of SAE 30 oil. What is its terminal velocity?(b) If the sphere is instead dropped into a different oil of the same density but develops a terminal speed of 1 cm/s, what is the oil’s viscosity?
In a production woodworking shop, 50-µm spherical dust particles were blown into the air while a piece of oak furniture was being sanded.(a) What is the terminal velocity of the particles as they fall through the air?(b) Neglecting air currents that are present, how long would it take the cloud of
A small water droplet in a mist of air is approximated as being a sphere of diameter 1.5 mil. Calculate the terminal velocity as it falls through still air to the ground. Is it reasonable to neglect the buoyancy force in this instance?
A steel storage tank is filled with gasoline. The tank has partially corroded on its inside, and small particles of rust have contaminated the fuel. The rust particles are approximately spherical, and they have a mean diameter of 25 µm and density of 5.3 g/cm3.(a) What is the terminal velocity of
Using the volcanic flow model and flow parameters from Problem P6.20, prepare two charts.(a) On one chart, plot the flow velocity in mph as a function of the slope, varying the slope from 08 to 908.(b) On the other chart, plot the fl ow velocity in mph as a function of the flow thickness, varying
(a) For a 1.25-in.-diameter pipe, what is the maximum volumetric flow rate at which water can be pumped and the flow will remain laminar? Express your result in the dimensions of gallons per minute.(b) What would be the maximum fl ow rate for SAE 30 oil?
At any time, approximately 20 volcanoes are actively erupting on the Earth, and 50–70 volcanoes erupt each year. Over the past 100 years, an average of 850 people have died each year from volcano eruptions. As scientists and engineers study the mechanics of lava flow, accurately predicting the
Assume that the fuel lines for each engine in the Boeing Dreamliner of Problem P6.17 are 7/8 in. in diameter and that the density and viscosity of jet fuel are 800 kg/m3 and 8.0 x 10-3 kg/(m ∙ s), respectively. Calculate the average velocity of the fuel in m/s and the Reynolds number of this
The Boeing 787 Dreamliner is billed to be 20% more fuel efficient than the comparable Boeing 767 and will fly at Mach 0.85. The midsize Boeing 767 has a range of 12,000 km, a fuel capacity of 90,000 L, and flies at Mach 0.80. Assume the speed of sound is 700 mph, and calculate the projected
(a) Determine the volumetric flow rate of blood in the artery of Problem P6.15.(b) Calculate the maximum velocity of blood across the artery’s cross section.(c) Determine the amount by which the blood pressure decreases along each 10-cm length of the artery.Problem P6.15The average velocity of
The average velocity of blood flowing in a certain 4-mm-diameter artery in the human body is 0.28 m/s. Calculate the Reynolds number and determine whether the flow is laminar or turbulent. The viscosity and density of blood are approximately 4 cP and 1.06 Mg/m3, respectively.
For the parabolic pressure profile in Equation (6.7), show that the average flow velocity is half the maximum value [Equation (6.11)].Equation 6.7Equation 6.11 (1 – (5) (Special case: Re < 2000) v = Vmax R
In a pipeline that connects a production oilfield to a tanker terminal, oil having density 1.85 slug/ft3 and viscosity 6 x 10−3 slug/(ft · s) flows through a 48-in.-diameter pipeline at 6 mph. What is the Reynolds number? Is the flow laminar or turbulent?
Water flows through a 5-cm-diameter pipe at the average velocity of 1.25 m/s.(a) In the dimensions of L/s, what is the volumetric flow rate?(b) If the diameter of the pipe is reduced by 20% at a constriction, by what percentage does the water’s velocity change?
Examine the transition between the laminar and turbulent flows of water by sketching the stream of water that exits from a faucet (without an aerator) or hose (without a nozzle). You can control the velocity of the stream by adjusting the water valve.(a) Make sketches of the flow for four different
Scuba divers carry ballast weights to have neutral buoyancy. At that condition, the buoyancy force on the diver exactly balances weight, and there is no tendency either to float toward the surface or to sink. In freshwater, a certain diver carries 10 lb of lead alloy ballast of density 1.17 × 104
An ancient king’s supposedly golden crown had a mass of 3 kg, but it was actually made by a dishonest metal smith from an equal mix of gold (1.93 × 104 kg/m3) and silver (1.06 × 104 kg/m3).(a) Suppose that Archimedes suspended the crown from a string and lowered it into water until it was
Make an order-of-magnitude estimate for a safety floatation device that can be used by children who are playing in a swimming pool. The design concept is for one inflatable, annular, plastic balloon to slide over each of the child’s arms and up to the shoulder. Take into account the child’s
For the system in Problem P6.6, suppose your design requirement was to minimize the force necessary to hold the gate closed. Would you rather put the hinge at the top of the gate or at the bottom? Support your answer.Problem P6.6A 6-m-high, 4-m-wide rectangular gate is located at the end of an open
A 6-m-high, 4-m-wide rectangular gate is located at the end of an open freshwater tank (Figure P6.6). The gate is hinged at the top and held in place by a force F. From Equation (6.4), the pressure is proportional to the depth of the water, and the average pressure pavg exerted on the gate by the
Blood pressure is conventionally measured in the dimensions of millimeters in a column of mercury, and the readings are expressed as two numbers, for example, 120 and 80. The first number is called the systolic value, and it is the maximum pressure developed as the heart contracts. The second
The pressure at the bottom of an 18-ft-deep storage tank for gasoline is how much greater than at the top? Express your answer in the units of psi.
The fuel tank on a sport-utility wagon holds 14 gal of gasoline. How much heavier is the automobile when the tank is full compared to when it is empty?
Michael Phelps won a record-setting 8 gold medals at the 2008 Beijing Olympics. Now imagine if Phelps had competed in a pool filled with pancake syrup. Would you expect his race times to increase, decrease, or stay the same? Research the issue and prepare an approximately 250- word report
Convert the viscosity of mercury (1.5 x 10-3 kg/(m · s)) to the dimensions of slug/(ft · s) and centipoise.
Using the bridge repair system in Problem P5.15, develop two additional two dimensional configurations that utilize different suspension arrangements. The following design requirements must be met: Two-level access to the bridge must be provided with the top platform at 90 in. below the road and
Plates and rods are frequently used to help rehabilitate broken bones (Figure P5.33). Calculate the shear stress in the lower 5-mm-diameter biomedical bolt if it is supporting a 1300-N force from the bone.Figure P5.33 1300 N
Compound lever shears cut through a piece of wire at A (Figure P5.32).(a) By using the free body diagram of handle CD, determine the magnitude of the force at rivet D.(b) Referring to the magnifi ed cross-sectional drawing of the connection at D, determine the shear stress in the rivet.(c) If the
A machinist squeezes the handle of visegrip pliers while loosening a frozen bolt (Figure P5.31). The connection at point A, which is shown in a magnified cross-sectional view, supports a 4.1-kN force.(a) Determine the shear stress in the 6-mm-diameter rivet at A.(b) Determine the factor of safety
A 3/8 -in.-diameter bolt connects the marine propeller to a boat’s 1 1/4 -in. driveshaft (Figure P5.30). To protect the engine and transmission if the propeller accidentally strikes an underwater obstacle, the bolt is designed to be cut when the shear stress acting on it reaches 25 ksi. Determine
For the exercise of Problem P5.28, and for the most conservative design, at what location on the step should you specify in your calculation that the 200-lb person stand? Determine the rivet diameter for that loading condition.Problem P5.28A small stepladder has vertical rails and horizontal steps
A small stepladder has vertical rails and horizontal steps formed from a C-section aluminum channel (Figure P5.28). Two rivets, one in front and one in back, secure the ends of each step. The rivets attach the steps to the left- and right-hand rails. A 200-lb person stands in the center of a step.
Recent technological advances have allowed for the production of graphene, which is a sheet of carbon atoms one atom thick, densely packed into a honeycomb structure. This material has excellent electrical, thermal, and optical properties, making it an ideal candidate for the design of electronic
Structural steel and stainless steel are both primarily made of iron. Why doesn’t stainless steel rust? Research the issue and prepare an approximately 250-word report describing the reason. Cite at least three references for your information.
A plastic pipe carries deionized water in a microelectronics clean room, and one end of it is capped (Figure P5.25). The water pressure is p0 = 50 psi, and the cap is attached to the end of the pipe by an adhesive. Calculate the shear stress τ present in the adhesive.Figure P5.25 Line pressure
A spur gear transmits 35 N · m of torque to the 20-mm-diameter driveshaft. The 5-mm-diameter setscrew threads onto the gear’s hub, and it is received in a small hole that is machined in the shaft. Determine the shear stress in the screw along the shear plane B–B (Figure P5.24).Figure P5.24 B
The tie-down mount in Figure P5.23 is bolted to the deck of a cargo truck and restrains the steel cable under 1.2 kN of tension. Determine the shear stress in the 6-mm-diameter bolt. Neglect the small horizontal and vertical offset distances between the bolt and the cable.Figure P5.23 1.2 kN 50°
A detailed view is shown for the connection B in the concrete trough from Problem P4.17 in Chapter 4 (Figure P5.22). Determine the shear stress acting in the shackle’s 3/8 -in. bolt.Figure P5.22Problem 14.7A circular rod of length 25 cm and diameter 8 mm is made of 1045 grade steel.(a) Calculate
A 600-lb force acts on the vertical plate, which in turn is connected to the horizontal truss by five 3/16 -in.-diameter rivets (Figure P5.21).(a) If the rivets share the load equally, determine the shear stress in them.(b) In a worst-case scenario, four of the rivets have corroded, and the load is
The small steel plate is connected to the right angle bracket by a 10-mm diameter bolt (Figure P5.20). Determine the tensile stress at point A in the plate and the shear stress in the bolt.Figure P5.20 6 mm 15 kN 10 mm A 15 kN 20 mm
Adhesive tape is capable of supporting relatively large shear stress, but it is not able to support significant tensile stress. In this problem, you will measure the shear strength of a piece of tape. Refer to Figure P5.19.(a) Cut about a dozen segments of tape having identical length L and width
Find a real physical example of a mechanical structure or machine that has shear stress present.(a) Make a clear, labeled drawing of the situation.(b) Estimate the dimensions of the structure or machine and the magnitudes and directions of the forces that act on it. Show these on the drawing.
An engineer determines that a 40-cm-long rod of 1020 grade steel will be subjected to a tension of 20 kN. The following two design requirements must be met: The stress must remain below 145 MPa, and the rod must stretch less than 0.125 mm. Determine an appropriate value for the rod’s diameter to
For the system in Problem P5.15, assume that two 180-lb workers are going to be standing on the system to repair a bridge, one on each platform. The following design requirement must be met: The stretch of each cable must be less than 0.01 in. at the worst-case loading condition for each cable.
A two-tier system to repair bridge infrastructures is supported by two steel cables for each platform (Figure P5.15). All the support cables have a diameter of 0.50 in. Assume the applied loads are at the midpoint of each platform. Determine how much each cable stretches at points A–D.Figure
A circular rod of length 25 cm and diameter 8 mm is made of 1045 grade steel.(a) Calculate the stress and strain in the rod, and its extension, when it is subjected to 5 kN of tension.(b) At what force would the rod begin to yield?(c) By what amount would the rod have to be stretched beyond its
The steel bolt and anchor assembly is used to reinforce the roof of a passageway in an underground coal mine (Figure P5.13). In installation, the bolt is tensioned to 5000 lb. Calculate the stress, strain, and extension of the bolt if it is formed from 1045 steel alloy.Figure P5.13 Coal seam
A 1-ft-long rod is made from the material of Problem P5.11. By what amount must the rod be stretched from its original length for it to begin yielding?Problem P5.11Determine the elastic modulus and the yield strength for the material having the stress–strain curve shown in Figure P5.11. Use the
Determine the elastic modulus and the yield strength for the material having the stress–strain curve shown in Figure P5.11. Use the 0.2% offset method.Figure P5.11 1600 1400 1200 名 1000 800 600 400 200 0.5 1 1.5 2 Strain, percent Stress, psi
The tires of the 4555-lb sedan are 6.5 in. wide (Figure P5.10). Each tire contacts the ground over a distance of 4.25 in. as measured along the vehicle’s length. Calculate the compressive stress between each tire and the road. The locations of the vehicle’s mass center and the wheelbase
An 8-mm-diameter aluminum rod has lines scribed on it that are exactly 10 cm apart (Figure P5.9, see on page 228). After a 2.11-kN force has been applied, the separation between the lines has increased to 10.006 cm.(a) Calculate the stress and strain in the rod.(b) To what total length has the rod
In a machine shop, the band saw blade is cutting through a work piece that is fed between the two guide blocks B (Figure P5.8). To what tension P should the blade be set if its stress is to be = ksi during use? Neglect the small size of the teeth relative to the blade’s width.Figure P5.8 P B 3
(a) By using either the vector algebra or polygon methods for finding a resultant, determine the magnitude of F that will cause the net effect of the three forces to act vertically.(b) For that value of F, determine the stress in the bolt’s 3/8 -in.-diameter straight shank.Figure P5.7 410 N F
As a machinist presses the handles of the compound-action bolt cutters, link AB carries a 7.5-kN force (Figure P5.6). If the link has a 14 x 4-mm rectangular cross section, calculate the tensile stress within it.Figure P5.6 7.5 kN A В 7.5 kN
When a 120-lb woman stands on a snow-covered trail, she sinks slightly into the snow because the compressive stress between her ski boots and the snow is larger than the snow can support without crumbling. Her cross-country skis are 65 in. long and 1 7/ 8 in. wide. After estimating the dimensions
A steel cable of diameter 3/16 in. is attached to an eyebolt and tensioned to 500 lb (Figure P5.4, see on page 226). Calculate the stress in the cable, and express it in the dimensions psi, ksi, Pa, kPa, and MPa.Figure P5.4 500 lb
Grade 1020 steel has a yield strength of 42 ksi and an elastic modulus of 30 Mpsi. Another grade of steel has a yield strength of 132 ksi. What is its elastic modulus?
A 1-Mg container hangs from a 15-mm-diameter steel cable. What is the stress in the cable?
Find a real physical example of a mechanical structure or machine that has tensile stress present.(a) Make a clear, labeled drawing of the situation.(b) Estimate the dimensions of the structure or machine and the magnitudes and directions of the forces that act on it. Show these on the drawing.
Many worldwide cities are in locations where extreme weather conditions can damage critical urban infrastructures. Select a representative at-risk city and design a structural system to shield the city. Develop a set of requirements and at least two different design concepts. Estimate the
Find an example of a structure or machine that has several forces acting on it.(a) Make a clear, labeled drawing of it.(b) Estimate the dimensions and the magnitudes and directions of the forces that act on it. Show these on your drawing. Briefly explain why you estimate the dimensions and forces
Two pots of food are being cooked on a solar cooker (Figure P4.32). The smaller pot weighs 4 lb, and the larger pot weighs 9 lb. Also, due to the thermal expansion of the parabolic reflector, a horizontal force of 0.5 lb is exerted outward on the two supports. Determine the magnitude of the
A portable music player is sitting in a docking station (Figure P4.31). The docking station has a mass of 500 g and the player, 100 g. Determine the reaction forces at the two supports.Figure P4.31 65 mm 70 mm 60 150 mm
Ball bearings support a shaft at points A and B (Figure P4.30). The shaft is used to transmit power between two V-belts that apply forces of 1 kN and 1.4 kN to the shaft. Determine the magnitudes and directions of the forces acting on the bearings.Figure P4.30 A 1 kN A B 1.4 kN 6 cm 6 ст 6 cm
Horizontal and vertical forces act on the pillow-block bearing as it supports a rotating shaft (Figure P4.29). Determine the magnitude of the resultant force and its angle relative to horizontal. Is the resultant force on the bearing a thrust or radial force?Figure P4.29 150 lb 85 lb 1.
The rolling-element bearings in a pillow-block bearing are contained within the housing block, which in turn can be bolted to another surface. Two radial forces act on the pillow-block bearing as shown (Figure P4.28).(a) Can the value of F be adjusted so that the resultant of the two forces is
A multipurpose utility tool grips a cotter pin at A while 15-lb forces are applied to the handles (Figure P4.27).(a) Complete the free body diagram of the combined upper jaw and lower handle assembly, which has been only partially drawn.(b) Calculate the force acting at A.(c) Alternatively, how
A handrail, which weighs 120 N and is 1.8 m long, was mounted to a wall adjacent to a small set of steps (Figure P4.26). The support at A has broken, and the rail has fallen about the loose bolt at B so that one end now rests on the smooth lower step.(a) Draw a free body diagram of the handrail.(b)
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