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physics
college physics 2nd
College Physics 2nd Edition OpenStax - Solutions
Calculate the change in length of the upper leg bone (the femur) when a 70.0 kg man supports 62.0 kg of his mass on it, assuming the bone to be equivalent to a uniform rod that is 40.0 cm long and 2.00 cm in radius.StrategyThe force is equal to the weight supported, or F = mg (62.0 kg) (9.80 m/s²)
(a) What is the maximum frictional force in the knee joint of a person who supports 66.0 kg of her mass on that knee?(b) During strenuous exercise it is possible to exert forces to the joints that are easily ten times greater than the weight being supported. What is the maximum force of friction
When you push a piece of chalk across a chalkboard, it sometimes screeches because it rapidly alternates between slipping and sticking to the board. Describe this process in more detail, in particular explaining how it is related to the fact that kinetic friction is less than static friction. (The
Find the mass of the picture hanging from a steel nail as shown in Figure 5.17, given that the nail bends only 1.80 μm. (Assume the shear modulus is known to two significant figures.)StrategyThe force on the nail (neglecting the nail’s own weight) is the weight of the picture w. If we can find
Suppose you have a 120-kg wooden crate resting on a wood floor.(a) What maximum force can you exert horizontally on the crate without moving it?(b) If you continue to exert this force once the crate starts to slip, what will the magnitude of its acceleration then be?
Athletes such as swimmers and bicyclists wear body suits in competition. Formulate a list of pros and cons of such suits.
Calculate the fractional decrease in volumefor seawater at 5.00 km depth, where the force per unit area is 5.00 × 107 N/m2. Strategy ΔΙ (18) V
(a) If half of the weight of a small 1.00 x 103 kg utility truck is supported by its two drive wheels, what is the magnitude of the maximum acceleration it can achieve on dry concrete?(b) Will a metal cabinet lying on the wooden bed of the truck slip if it accelerates at this rate?(c) Solve both
Two expressions were used for the drag force experienced by a moving object in a liquid. One depended upon the speed, while the other was proportional to the square of the speed. In which types of motion would each of these expressions be more applicable than the other one?
Consider the 65.0-kg ice skater being pushed by two others shown in Figure 5.19.(a) Find the direction and magnitude of Ftot, the total force exerted on her by the others, given that the magnitudes F1 and F2 are 26.4 N and 18.6 N, respectively.(b) What is her initial acceleration if she is
A team of eight dogs pulls a sled with waxed wood runners on wet snow (mush!). The dogs have average masses of 19.0 kg, and the loaded sled with its rider has a mass of 210 kg.(a) Calculate the magnitude of the acceleration starting from rest if each dog exerts an average force of 185 N backward on
As cars travel, oil and gasoline leaks onto the road surface. If a light rain falls, what does this do to the control of the car? Does a heavy rain make any difference?where B is the bulk modulus, V0 is the original volume, and F/A is the force per unit area applied uniformly inward on all
Why can a squirrel jump from a tree branch to the ground and run away undamaged, while a human could break a bone in such a fall?
The elastic properties of the arteries are essential for blood flow. Explain the importance of this in terms of the characteristics of the flow of blood (pulsating or continuous).
Show that the acceleration of any object down an incline where friction behaves simply (that is, where fk = μk N) is a = g(sin θ- μk cos θ). Note that the acceleration is independent of mass and reduces to the expression found in the previous problem when friction becomes negligibly small (μk
What are you feeling when you feel your pulse? Measure your pulse rate for 10 s and for 1 min. Is there a factor of 6 difference?
Examine different types of shoes, including sports shoes and thongs. In terms of physics, why are the bottom surfaces designed as they are? What differences will dry and wet conditions make for these surfaces?
If an object is to rest on an incline without slipping, then friction must equal the component of the weight of the object parallel to the incline. This requires greater and greater friction for steeper slopes. Show that the maximum angle of an incline above the horizontal for which an object will
Would you expect your height to be different depending upon the time of day? Why or why not?
Calculate the maximum deceleration of a car that is heading down a 6°slope (one that makes an angle of 6° with the horizontal) under the following road conditions. You may assume that the weight of the car is evenly distributed on all four tires and that the coefficient of static friction is
Would you expect a large or small stress to be required to deform a spider web? Why is this elasticity an important feature for a spider web?
Explain why pregnant women often suffer from back strain late in their pregnancy.
An old carpenter’s trick to keep nails from bending when they are pounded into hard materials is to grip the center of the nail firmly with pliers. Why does this help?
A freight train consists of two 8.00 x 105-kg engines and 45 cars with average masses of 5.50 x 105 kg.(a) What force must each engine exert backward on the track to accelerate the train at a rate of 5.00 x 10-2 m/s if the force of friction is 7.50 x 105 N, assuming the engines exert identical
Consider the 52.0-kg mountain climber in Figure 5.20.(a) Find the tension in the rope and the force that the mountain climber must exert with her feet on the vertical rock face to remain stationary. Assume that the force is exerted parallel to her legs. Also, assume negligible force exerted by her
When a glass bottle full of vinegar warms up, both the vinegar and the glass expand, but vinegar expands significantly more with temperature than glass. The bottle will break if it was filled to its tightly capped lid. Explain why, and also explain how a pocket of air above the vinegar would
Define normal force. What is its relationship to friction when friction behaves simply?
Critical Thinking Two boxes of equal mass slide start from rest and slide with different horizontal applied forces across frictionless surfaces to reach the same distance away. Box A has a horizontal force of three times that of box B.(a) Which box is traveling faster at this distance away from the
A physics major is cooking breakfast when he notices that the frictional force between his steel spatula and his Teflon frying pan is only 0.200 N. Knowing the coefficient of kinetic friction between the two materials, he quickly calculates the normal force. What is it?
A contestant in a winter sporting event pushes a 45.0-kg block of ice across a frozen lake as shown in Figure 5.21(a).(a) Calculate the minimum force F he must exert to get the block moving.(b) What is the magnitude of its acceleration once it starts to move, if that force is maintained? 25
Repeat Exercise 5.18 with the contestant pulling the block of ice with a rope over his shoulder at the same angle above the horizontal as shown in Figure 5.21(b).Data given in Exercise 5.18A contestant in a winter sporting event pushes a 45.0-kg block of ice across a frozen lake as shown in Figure
The terminal velocity of a person falling in air depends upon the weight and the area of the person facing the fluid. Find the terminal velocity (in meters per second and kilometers per hour) of an 80.0-kg skydiver falling in a headfirst position with a cross-section area facing the fluid of 0.140
A 60-kg and a 90-kg skydiver jump from an airplane at an altitude of 6000 m, both falling in a headfirst position. Make some assumption on their frontal areas and calculate their terminal velocities. How long will it take for each skydiver to reach the ground (assuming the time to reach terminal
A 560-g squirrel with a cross-section area facing the fluid of 144 cm2 falls from a 5.0-m tree to the ground. Estimate its terminal velocity. (Use a drag coefficient for a horizontal skydiver.) What will be the velocity of a 56-kg person hitting the ground, assuming no drag contribution in such a
Using Stokes’ law, verify that the units for viscosity are kilograms per meter per second.
Calculate the speed a spherical rain drop would achieve falling from 5.00 km(a) In the absence of air drag(b) With air drag. Take the size across of the drop to be 4 mm, the density to be 1.00 x 103 kg/m3, and the cross-section area facing the fluid to be πr2.
By what factor does the drag force on a car increase as it goes from 65 to 110 km/h?
Critical Thinking Two spherical beads of the same mass fall at a constant speed due to a drag force. Bead A takes twice as long to fall the same distance as bead B.(a) Which of these beads has the larger radius?(b) Based on experimental data, an equation that fits the data is suggested for radius
The pole in Figure 5.22 is at a 90.0° bend in a power line and is therefore subjected to more shear force than poles in straight parts of the line. The tension in each line is 4.00 x 104 N, at the angles shown. The pole is 15.0 m tall, has an 18.0 cm diameter, and can be considered to have half
Find the terminal velocity of a spherical bacterium (diameter 2.00 m) falling in water. You will first need to note that the drag force is equal to the weight at terminal velocity. Take the density of the bacterium to be 1.10 × 103 kg/m3.
During a wrestling match, a 150 kg wrestler briefly stands on one hand during a maneuver designed to perplex her adversary. By how much does the upper arm bone shorten in length? The bone can be represented by a uniform rod 38.0 cm in length and 2.10 cm in radius.
(a) The "lead" in pencils is a graphite composition with a Young's modulus of about 1 x 109 N/m2. Calculate the change in length of the lead in an automatic pencil if you tap it straight into the pencil with a force of 4.0 N. The lead is 0.50 mm in diameter and 60 mm long.(b) Is the answer
TV broadcast antennas are the tallest artificial structures on Earth. In 1987, a 72.0-kg physicist placed himself and 400 kg of equipment at the top of one 610-m high antenna to perform gravity experiments. By how much was the antenna compressed, if we consider it to be equivalent to a steel
(a) By how much does a 65.0-kg mountain climber stretch her 0.800-cm diameter nylon rope when they hang 35.0 m below a rock outcropping?(b) Does the answer seem to be consistent with what you have observed for nylon ropes? Would it make sense if the rope were actually a bungee cord?
A 20.0-m tall hollow aluminum flagpole is equivalent in stiffness to a solid cylinder 4.00 cm in diameter. A strong wind bends the pole much as a horizontal force of 900 N exerted at the top would. How far to the side does the top of the pole flex?
Calculate the force a piano tuner applies to stretch a steel piano wire 8.00 mm, if the wire is originally 0.850 mm in diameter and 1.35 m long.
A vertebra is subjected to a shearing force of 500 N. Find the shear deformation, taking the vertebra to be a cylinder 3.00 cm high and 4.00 cm in diameter.
A disk between vertebrae in the spine is subjected to a shearing force of 600 N. Find its shear deformation, taking it to have the shear modulus of 1 x 109 N/m2. The disk is equivalent to a solid cylinder 0.700 cm high and 4.00 cm in diameter.
When using a pencil eraser, you exert a vertical force of 6.00 N at a distance of 2.00 cm from the hardwood-eraser joint. The pencil is 6.00 mm in diameter and is held at an angle of 20.0 to the horizontal.(a) By how much does the wood flex perpendicular to its length?(b) How much is it compressed
To consider the effect of wires hung on poles, we take data from Example 4.8, in which tensions in wires supporting a traffic light were calculated. The left wire made an angle 30.0° below the horizontal with the top of its pole and carried a tension of 108 N. The 12.0 m tall hollow aluminum pole
(a) When water freezes, its volume increases by 9.05% (that is, ΔV/V0 = 9.05 ×10-2). What force per unit area is water capable of exerting on a container when it freezes? (It is acceptable to use the bulk modulus of water in this problem.)(b) Is it surprising that such forces can fracture engine
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