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physics
college physics 2nd
Questions and Answers of
College Physics 2nd
Snakes and other reptiles that live on land warm up in the sun. Their bodies can reach temperatures well above the ambient air temperature. But fish don’t do this. Most fish are at nearly the same
Male emperor penguins spend the long Antarctic night on the ice. They keep from freezing with exquisite thermal insulation. Their insulation is so effective that the surface temperature of their
Suppose you start your day in Denver, on a cool 10°C spring day. The local atmospheric pressure is 85 kPa. You fill your car’s tires until the gauge shows 210 kPa (about 30 psi). You then drive up
You can buy an expensive frying pan that is made of copper but has a handle made of stainless steel. Why are different metals used for the part of the pan that touches the stove and for the part that
On a chilly 10°C day, you quickly take a deep breath—all your lungs can hold, 4.0 L. The air warms to your body temperature of 37°C. If the air starts at a pressure of 1.0 atm, and you hold the
If a person’s lungs are compromised, they can use supplemental oxygen to increase the concentration of oxygen in their lungs. Explain how this helps increase oxygen uptake.
A football is inflated in the locker room before the game. The air warms as it is pumped, so it enters the ball at a temperature of 27°C. The ball is inflated to a gauge pressure of 13 psi. The ball
Many fish maintain buoyancy with a gas-filled swim bladder. The pressure inside the swim bladder is the same as the outside water pressure, so when a fish descends to a greater depth, the gas
Suppose you inflate your car tires to 35 psi on a 20°C day. Later, the temperature drops to 0°C. What is the pressure in your tires now?
When you apply the brakes on your car, the kinetic energy of your vehicle is transformed into thermal energy in your brake disks. During a mountain descent, a 28.00-cm-diameter iron brake disk heats
In the chapter, you saw that bridges often have expansion joints to account for the changes in size due to temperature changes. Suppose a bridge is supported by steel girders; the central span has a
When people exercise, they report feeling exhaustion when their body temperature rises to 39.7°C. A 68 kg man is running at 15 km/h on a hot, muggy day—so hot and muggy that he can’t lose any
Dogs keep themselves cool by panting, rapidly breathing air in and out. Panting results in evaporation from moist tissues of the airway and lungs, which cools the animal. Measurements show that, on a
The Bodø NATO base in northern Norway uses a heat pump to extract heat from ocean water. 7.0°C ocean water is continuously drawn into the system, heat is extracted, and the water is returned to the
If you pour whisky over ice, the ice will cool the drink, but it will also dilute it. A solution is to use whisky stones. Suppose Ernest pours 55 g of whisky at 22°C room temperature, and then adds
It’s possible to boil water by adding hot rocks to it, a technique that has been used in many societies over time. If you heat a rock in the fire, you can easily get it to a temperature of 500°C.
You draw in a deep breath on a chilly day, inhaling 3.0 L of 0°C air. If the pressure in your lungs is a constant 1.0 atm, how much heat must your body supply to warm the air to your 37°C internal
A 30 kg male emperor penguin under a clear sky in the Antarctic winter loses very little heat to the environment by convection; its feathers provide very good insulation. It does lose some heat
A nerve impulse is propagated across a synapse when the neurotransmitter acetylcholine is released from the pre-synaptic membrane and diffuses across the 20-nm-wide synaptic cleft to the
Your heart does work to pump blood through your body. Each minute, 5.0 L of blood travels through your circulatory system. The pressure drops from 16 kPa as it exits the heart to approximately zero
When you put on the brakes on your bicycle, friction heats the steel rims of your wheels. Could this heating be a problem? Suppose a 65 kg cyclist with a 15 kg bike is descending Trail Ridge Road in
If you put a heavy load in a wheelbarrow, the force you apply to the handles is much less than the weight of the load and the wheelbarrow. To lift with the least force, you put the load toward the
When you carry shopping bags, rather than grasp the handles with your hand as in Figure Q8.14a, you might choose to put them over your arm and slide the handle toward your elbow as in Figure Q8.14b.
You can apply a much larger bite force with your molars, in the back of your mouth, than with your incisors, at the front of your mouth. Explain why this is so.
An isometric exercise is one in which the joint angle does not change during the application of muscle force. For instance, you can join your hands together, pushing down with one hand and pushing up
A hippo’s body is 4.0 m long with front and rear feet located as in Figure P8.8. The hippo carries 60% of its weight on its front feet. How far from its tail is the hippo’s center of gravity? 0.5
A bicycle mechanic is checking a road bike’s chain. He applies a 45 N force to a pedal at the angle shown in Figure P8.10 while keeping the wheel from rotating. The pedal is 17 cm from the center
A 60 kg diver stands at the end of a 30 kg springboard, as shown in Figure P8.11. The board is attached to a hinge at the left end but simply rests on the right support. What is the magnitude of the
A bike chain can support a tension of no more than 9800 N. The pedal connects to a crank 17 cm from the axle, and the gear pulling the chain has a 9.1 cm radius. When riding at a constant speed, with
The four wheels of a car are connected to the car’s body by spring assemblies that let the wheels move up and down over bumps and dips in the road. When a 68 kg (about 150 lb) person sits on the
A passenger railroad car has a total of 8 wheels. Springs on each wheel compress—slightly—when the car is loaded. Ratings for the car give the stiffness per wheel (the spring constant, treating
Dynamic climbing ropes are designed to be quite pliant, allowing a falling climber to slow down over a long distance. The graph in Figure P8.30 shows forceversus-strain data for an 11-mm-diameter
Static climbing ropes are designed to be relatively stiff so that they stretch less than dynamic ropes. To meet a certain specification, an 11-mm-diameter rope must experience a maximum elongation of
A mineshaft has an ore elevator hung from a single braided cable of diameter 2.5 cm. Young’s modulus of the cable is 10 × 1010 N/m2 . When the cable is fully extended, the end of the cable is 800
To penetrate armor, a projectile’s point concentrates force in a small area, creating a stress large enough that the armor fails. A species of jellyfish launches a pointed needle that can penetrate
You’ve just put a new wood floor in your house. An object will dent the flooring if the stress—the force divided by the area—exerted by the object is great enough. Who is more likely to dent
A woman is pushing a load in a wheelbarrow, as in Figure P8.44. The combined mass of the wheelbarrow and the load is 110 kg, with a center of gravity 0.25 m behind the axle. The woman supports the
Figure P8.45 shows the operation of a garlic press. The lower part of the press is held steady, and the upper handle is pushed down, thereby crushing a garlic clove through a screen. Approximate
Consider a rower in a scull as in Figure P8.46. The oars aren’t accelerating, and they are rotating at a constant speed, so the net force and net torque on the oars are zero. An oar is 2.8 m long,
If you stand on one foot while holding your other leg up behind you, your muscles apply a force to hold your leg in this raised position. We can model this situation as in Figure P8.48. The leg
Dogs—like many animals—stand and walk on their toes. A photo of the rear foot of a dog is shown in Figure P8.50a; Figure P8.50b shows the bones of the leg and foot along with relevant distances.
An 85 kg man stands in a very strong wind moving at 14 m/s at torso height. As you know, he will need to lean in to the wind, and we can model the situation to see why. Assume that the man has a mass
DNA molecules are typically folded tightly. Stretching a strand of DNA means straightening it, and the molecules resist this straightening. Investigators can attach beads to the ends of a strand of
You are bowling with a 10-pound ball that you throw at 10 mph, and you’ve decided that you need to hit the pins with a ball that has more momentum. What are two possible changes you could make?
When you catch a water balloon, it’s best to start with your hand in motion, moving with the balloon, and then gradually slow it to rest. Why is this approach desirable?
When you leap down from a high perch, you have a gentler landing with less force if you bend your knees as you land. Use the principles of impulse and momentum to explain why this approach reduces
Students in a technology class are racing cars propelled by carbon dioxide cartridges. A burst of gas is released when the seal of the cartridge is broken, and this propels the car down the track.
In the past, asteroids striking the earth have produced disastrous results. If we discovered an asteroid on a collision course with the earth, we could, in principle, deflect it and avoid an impact
In the playground game of tetherball, a ball tied to a rope circles a pole, wrapping the rope around the pole is it goes. Opponents compete to wrap the ball around the pole in one direction or the
If you jump from a diving board and find that your body is rotating forward, you can spin your arms to stop the rotation and make your body land feet first. Explain in which direction you would
A dancer leaping into the air and trying for the maximum possible vertical height will move her arms upward as she is pushing off with her legs, putting her arms in rapid upward motion before she
Two physics students are doing a side competition during a game of bowling, seeing who can toss a ball with the larger momentum. The first bowler throws a 4.5 kg ball at 7.2 m/s. A second bowler
A large raindrop—the type that lands with a definite splat— has a mass of 0.014 g and hits your roof at a speed of 8.1 m/s.a. What is the magnitude of the impulse delivered to your roof?b. If
A billiard ball of mass 0.28 kg hits a second, identical ball at a speed of 7.2 m/s and comes to rest as the second ball flies off. The collision takes 250 μs. What is the average force on the first
A trap-jaw ant snaps its mandibles shut at very high speed, a good trait for catching small prey. But an ant can also slam its mandibles into the ground; the resulting force can launch the ant into
Investigators studying the effect of hitting a soccer ball with the head are using a force plate to look at the forces in ball collisions; the force when the ball hits a player’s head will be
Ferns spread spores instead of seeds, and some ferns eject the spores at surprisingly high speeds. One species accelerates 1.4 μg spores to a 4.5 m/s ejection speed in a time of 1.0 ms. What impulse
Climbing ropes stretch when they catch a falling climber, thus increasing the time it takes the climber to come to rest and reducing the force on the climber. In one standardized test of ropes, an 80
Squid rely on jet propulsion when a rapid escape is necessary. A 1.5 kg squid at rest pulls 0.10 kg of water into its mantle, then ejects this water at a remarkable 45 m/s. Right after this ejection,
Some species of jellyfish use jet propulsion to get around, a much gentler form of jet propulsion than squid use. A small jellyfish takes water into its bell; the total mass of jellyfish and water is
If you free the cork in a highly pressurized champagne bottle, the resulting launch of the cork will, in principle, cause the bottle to recoil. A filled champagne bottle has a mass of 1.8 kg. The
In a football game, a 90 kg receiver leaps straight up in the air to catch the 0.42 kg ball the quarterback threw to him at a vigorous 21 m/s, catching the ball at the highest point in his jump.
Casey is driving a 1600 kg car toward the east. She goes through an intersection at a speed of 16 m/s (approximately 35 mph), the speed limit on both roads of the intersection. Kerry is driving a car
A 110 kg linebacker running at 2.0 m/s and an 82 kg quarterback running at 3.0 m/s have a head-on collision in midair. The linebacker grabs and holds onto the quarterback. Who ends up moving forward
A canoe is designed to have very little drag when it moves along its length. Riley, mass 52 kg, sits in a 21 kg canoe in the middle of a lake. She dives into the water off the front of the canoe,
A water pipe in a building delivers 1000 liters (with mass 1000 kg) of water per second. The water is moving through the pipe at 1.4 m/s. The pipe has a 90° bend, and the pipe will require a
You swing a weight attached to a string in a vertical circle. At the top of the circle the string just barely goes slack for an instant. At this point the centripetal acceleration of the weight
In the Skycoaster amusement park ride, riders are suspended from a tower by a long cable. A second cable then lifts them until they reach the starting position indicated in Figure P5.3. The lifting
Bethany, who weighs 560 N, lies in a hammock suspended by ropes tied to two trees. One rope makes an angle of 45° with the ground; the other makes an angle of 30°. Find the tension in each of the
In the winter sport of curling, two teams alternate sliding 20 kg stones on an icy surface in an attempt to end up with the stone closest to the center of a target painted on the ice. During one
The acceleration of the spacecraft in which the Apollo astronauts took off from the moon was 3.4 m/s2 . On the moon, g = 1.6 m/s2 .What was the apparent weight of a 75 kg astronaut during takeoff?
A dump truck, whose bed is made of steel, holds an old steel watering trough. The bed of the truck is slowly raised until the trough begins to slide. What is the acceleration of the trough as it
A vendor at the local art fair ties her tent to the concrete-filled coffee can shown in Figure P5.34. A stiff breeze comes up and the string becomes taut. What is the maximum value that the string
Oceanographers use submerged sonar systems, towed by a cable from a ship, to map the ocean floor. In addition to their downward weight, there are buoyant forces and forces from the flowing water that
At its widest point, the diameter of a bottlenose dolphin is 0.50 m. Bottlenose dolphins are particularly sleek, having a drag coefficient of only about 0.090.a. What is the drag force acting on
The most dangerous particles in polluted air are those with diameters less than 2.5 mm because they can penetrate deeply into the lungs. A 15-cm-tall closed container holds a sample of polluted air
What is the magnitude of the acceleration of a skydiver who is currently falling at one-half his eventual terminal speed?
A Jeep is stuck in the mud. The driver has a winch that can pull on its cable with a force of 40,000 N. The driver loops the cable through a pulley attached to a tree, then attaches the end of the
You probably think of wet surfaces as being slippery. Surprisingly, the opposite is true for human skin, as you can demonstrate by sliding a dry versus a slightly damp fingertip along a smooth
In rock climbing, various rope and pulley systems have been devised to help haul up heavy loads, including injured climbers. A rescuer is hauling up an injured climber who weighs 660 N using the rope
The earth, with a radius of 6.4 × 106 m, rotates on its axis once a day. What is the speed of a person standing on the equator, due to the earth’s rotation?
The force on an airplane’s wing from the air flowing past it is mostly perpendicular to the wing’s flat surface; this is the force that holds the plane aloft in level flight. Given this fact, why
Tarzan hangs from a vine without it breaking. But when he swings on the same vine starting from a high branch, the vine snaps at the bottom of his swing. Explain why this happens.
The California sea lion is capable of making extremely fast, tight turns while swimming underwater. In one study, scientists observed a sea lion making a circular turn with a radius of 0.35 m while
On a roller coaster loop-the-loop the riders are upside-down at the top of the loop, while on a Ferris wheel the riders are upright at the top. Suppose a Ferris wheel and the loop of a roller coaster
Baseball pitching machines are used to fire baseballs toward a batter for hitting practice. In one kind of machine, the ball is fed between two wheels that are rapidly rotating in opposite
Astronauts in the International Space Station must work out every day to counteract the effects of weightlessness. Researchers have investigated if riding a stationary bicycle while experiencing
In addition to their remarkable top speeds of almost 60 mph, cheetahs have impressive cornering abilities. In one study, the maximum centripetal acceleration of a cheetah was measured to be 18 m/s2 .
An object’s apparent weight is slightly less when it is at the equator than when it is at the North Pole. Explain why this is so.
A wind turbine has 12,000 kg blades that are 38 m long. The blades spin at 22 rpm. If we model a blade as a point mass at the midpoint of the blade, what is the inward force necessary to provide each
The spin cycle of a clothes washer extracts the water in clothing by greatly increasing the water’s apparent weight so that it is efficiently squeezed through the clothes and out the holes in the
In the very Dutch sport of Fierljeppen, athletes run up to a long pole and then use it to vault across a canal. At the very top of his arc, a 55 kg vaulter is moving at 2.5 m/s and is 5.1 m from the
You’re driving your new sports car at 75 mph over the top of a hill that has a radius of curvature of 525 m. What fraction of your normal weight is your apparent weight as you crest the hill?
In a car’s suspension system, each wheel is connected to a vertical spring; these springs absorb shocks when the car travels on bumpy roads. In one car, each spring has a spring constant of 5.0 ×
Just before it landed on the moon, the Apollo 12 lunar lander had a mass of 7200 kg. What rocket thrust was necessary to have the lander touch down with zero acceleration?
The gravitational constant G was first measured accurately by Henry Cavendish in 1798. He used an exquisitely sensitive balance to measure the force between two lead spheres whose centers were 0.23 m
In 2014, a space probe approached the rocky core of the comet Churyumov–Gerasimenko, which is only a few km in diameter. The probe then entered orbit around the comet at a distance of 30 km. The
Mars has two moons, Phobos and Deimos. Phobos orbits Mars at a distance of 9380 km from Mars’s center, while Deimos orbits at 23,500 km from the center. What is the ratio of the orbital period of
Mars’s moon Phobos orbits the planet at a distance of 9380 km from its center, and it takes 7 hours and 39 minutes to complete one orbit. What is the ratio of Mars’s mass to the mass of the earth?
The dwarf planet Praamzius is estimated to have a diameter of about 300 km and orbits the sun at a distance of 6.4 × 1012 m. What is its orbital period in years?
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