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physics
college physics a strategic approach 2nd
College Physics A Strategic Approach 2nd Edition Randall D. Knight, Brian Jones, Stuart Field - Solutions
Ethan, whose mass is 80 kg, stands at one end of a very long. stationary wheeled cart that has a mass of 500 kg. He then starts sprinting toward the other end of the cart. He soon reaches his top speed of 8.0 m/s, measured relative to the cart. What is the speed of the cart when Ethan has reached
The cars of a long coal train are filled by pulling them under a hopper, from which coal falls into the cars at a rate of 10,000 kg/s. Ignoring friction due to the rails, what is the aver- age force that the engine must exert on the coal train to keep it moving under the hopper at a speed of 0.50
Laura, whose mass is 35 kg, jumps horizontally off a 55 kg canoe at 1.5 m/s relative to the canoe. What is the canoe's speed just after she jumps?
A proton is shot at 5.0 x 107 m/s toward a gold target. The nucleus of a gold atom, with a mass 197 times that of the pro- ton, repels the proton and deflects it straight back with 90% of its initial speed. What is the recoil speed of the gold nucleus?
A 200 g puck revolves in a circle on a frictionless table at the end of a 50.0-cm-long string. The puck's angular momentum about the center of the circle is 3.00 kg • m2/s. What is the tension in the string?
Figure P9.71 shows a 100 g puck revolving in a 20-cm- radius circle on a frictionless table. The string passes through a hole in the center of the table and is tied to two 200 g weights. a. What speed does the puck need to support the two weights?b. The lower weight is a light bag filled with
Disk A, with a mass of 2.0 kg and a radius of 40 cm, rotates clockwise about a frictionless vertical axle at 30 rev/s. Disk B, also 2.0 kg but with a radius of 20 cm, rotates counterclockwise about that same axle, but at a greater height than disk A, at 30 rev/s. Disk B slides down the axle until
During an etiquette class, you walk slowly and steadily at 0.20 m/s for 2.5 m with a 0.75 kg book balanced on top of your head. How much work does your head do on the book?
The brake shoes of your car are made of a material that can tolerate very high temperatures without being damaged. Why is this so?
When you pound a nail with a hammer, the nail gets quite warm. Describe the energy transformations that lead to the addition of thermal energy in the nail.
The two ropes shown in the bird's-eye view of Figure P10.4 are used to drag a crate exactly 3 m across the floor. How much work is done by each of the ropes on the crate? 500 N FIGURE P10.4 T₂ T₁ 326 N 20⁰ √30⁰ 223 N
a. At the airport, you ride a "moving sidewalk" that carries you horizontally for 25 m at 0.70 m/s. Assuming that you were moving at 0.70 m/s before stepping onto the moving sidewalk and continue at 0.70 m/s afterward, how much work does the moving sidewalk do on you? Your mass is 60 kg. b. An
A boy flies a kite with the string at a 30° angle to the horizontal. The tension in the string is 4.5 N. How much work does the string do on the boy if the boy.a. Stands still? b. Walks a horizontal distance of 11 m away from the kite? c. Walks a horizontal distance of 11 m toward the kite?
A car is traveling at 10 m/s. a. How fast would the car need to go to double its kinetic energy? b. By what factor does the car's kinetic energy increase if its speed is doubled to 20 m/s?
Sam's job at the amusement park is to slow down and bring to a stop the boats in the log ride. If a boat and its riders have a mass of 1200 kg and the boat drifts in at 1.2 m/s, how much work does Sam do to stop it?
A ball of putty is dropped from a height of 2 m onto a hard floor, where it sticks. What object or objects need to be included within the system if the system is to be isolated during this process?
A 0.5 kg mass on a 1-m-long string swings in a circle on a hori- zontal, frictionless table at a steady speed of 2 m/s. How much work does the tension in the string do on the mass during one revolution? Explain.
The turntable in a microwave oven has a moment of inertia of 0.040 kg • m2 and is rotating once every 4.0 s. What is its kinetic energy?
Particle A has less mass than particle B. Both are pushed for- ward across a frictionless surface by equal forces for 1 s. Both start from rest. a. Compare the amount of work done on each particle. That is, is the work done on A greater than, less than, or equal to the work done on B? Explain. b.
An energy storage system based on a flywheel (a rotating disk) can store a maximum of 4.0 MJ when the flywheel is rotating at 20,000 revolutions per minute. What is the moment of inertia of the flywheel?
The meaning of the word "work" is quite different in physics from its everyday usage. Give an example of an action a person could do that "feels like work" but that does not involve any work as we've defined it in this chapter.
To change a tire, you need to use a jack to raise one corner of your car. While doing so, you happen to notice that pushing the jack handle down 20 cm raises the car only 0.2 cm. Use energy concepts to explain why the handle must be moved so far to raise the car by such a small amount.
You drop two balls from a tower, one of mass m and the other of mass 2m. Just before they hit the ground, which ball, if either, has the larger kinetic energy? Explain.
The world's fastest humans can reach speeds of about 11 m/s. In order to increase his gravitational potential energy by an amount equal to his kinetic energy at full speed, how high would such a sprinter need to climb?
A 72 kg bike racer climbs a 1200-m-long section of road that has a slope of 4.3°. By how much does his gravitational potential energy change during this climb?
A 1000 kg wrecking ball hangs from a 15-m-long cable. The ball is pulled back until the cable makes an angle of 25° with the vertical. By how much has the gravitational potential energy of the ball changed?
Sandy and Chris stand on the edge of a cliff and throw identical mass rocks at the same speed. Sandy throws her rock horizontally while Chris throws his upward at an angle of 45° to the horizontal. Are the rocks moving at the same speed when they hit the ground, or is one moving faster than the
How much energy can be stored in a spring with a spring constant of 500 N/m if its maximum possible stretch is 20 cm?
You are much more likely to be injured if you fall and your head strikes the ground than if your head strikes a gymnastics pad. Use energy and work concepts to explain why this is so.
A woman uses a pulley and a rope to raise a 20 kg weight to a height of 2 m. If it takes 4 s to do this, about how much power is she supplying? A. 100 W B. 200 W C. 300 W D. 400 W
A hockey puck sliding along frictionless ice with speed v to the right collides with a horizontal spring and compresses it by 2.0 cm before coming to a momentary stop. What will be the spring's maximum compression if the same puck hits it at a speed of 2v? A. 2.0 cm B. 2.8 cm C. 4.0 cm D. 5.6
A block slides down a smooth ramp, starting from rest at a height h. When it reaches the bottom it's moving at speed v. It then continues to slide up a second smooth ramp. At what height is its speed equal to v/2? A. h/4 B. h/2 C. 3h/4 D. 2h
A wrecking ball is suspended from a 5.0-m-long cable that makes a 30 angle with the vertical. The ball is released and swings down. What is the ball's speed at the lowest point? A. 7.7 m/s B. 4.4 m/s C. 3.6 m/s D. 3.1 m/s
Your friend's Frisbee has become stuck 16 m above the ground in a tree. You want to dislodge the Frisbee by throwing a rock at it. The Frisbee is stuck pretty tight, so you figure the rock needs to be traveling at least 5.0 m/s when it hits the Frisbee. If you release the rock 2.0 m above the
A fireman of mass 80 kg slides down a pole. When he reaches the bottom, 4.2 m below his starting point, his speed is 2.2 m/s. By how much has thermal energy increased during his slide?
A hockey puck is given an initial speed of 5.0 m/s. If the coefficient of kinetic friction between the puck and the ice is 0.05, how far does the puck slide before coming to rest? Solve this problem using conservation of energy.
A 1000 kg sports car accelerates from 0 to 30 m/s in 10 s. What is the average power of the engine?
In just 0.30 s, you compress a spring (spring constant 5000 N/m), which is initially at its equilibrium length, by 4.0 cm. What is your average power output?
In the winter sport of curling, players give a 20 kg stone a push across a sheet of ice. A curler accelerates a stone to a speed of 3.0 m/s over a time of 2.0 s. a. How much force does the curler exert on the stone? b. What average power does the curler use to bring the stone up to speed?
A 710 kg car drives at a constant speed of 23 m/s. It is subject to a drag force of 500 N. What power is required from the car's engine to drive the car.a. On level ground? b. Up a hill with a slope of 2.0?
An elevator weighing 2500 N ascends at a constant speed of 8.0 m/s. How much power must the motor supply to do this?
A marble slides without friction in a vertical plane around the inside of a smooth, 20-cm-diameter horizontal pipe. The marble's speed at the bottom is 3.0 m/s; this is fast enough so that the marble makes a complete loop, never losing contact with the pipe. What is its speed at the top?
A 20 kg child is on a swing that hangs from 3.0-m-long chains, as shown in Figure P10.52. What is her speed vi, at the bottom of the arc if she swings out to a 45° angle before reversing direction? 3.0 m 45° FIGURE P10.52
Suppose you lift a 20 kg box by a height of 1.0 m. a. How much work do you do in lifting the box? Instead of lifting the box straight up, suppose you push it up a 1.0-m-high ramp that makes a 30 degree angle with the horizontal, as shown in Figure P10.53. Being clever, you choose a ramp with no
The sledder shown in Figure P10.55 starts from the top of a frictionless hill and slides down into the valley. What initial speed vi does the sledder need to just make it over the next hill? 30 m FIGURE P10.55 T 42 m 1 1
In a physics lab experiment, a spring clamped to the table shoots a 20 g ball horizontally. When the spring is compressed 20 cm, the ball travels horizontally 5.0 m and lands on the floor 1.5 m below the point at which it left the spring. What is the spring constant?
In an amusement park water slide, people slide down an essentially frictionless tube. They drop 3.0 m and exit the slide, moving horizontally, 1.2 m above a swimming pool. What horizontal distance do they travel from the exit point before hitting the water? Does the mass of the person make any
Two coupled boxcars are rolling along at 2.5 m/s when they collide with and couple to a third, stationary boxcar. a. What is the final speed of the three coupled boxcars? b. What fraction of the cars' initial kinetic energy is trans- formed into thermal energy?
How long will it take a rock dropped from 2.0 m above the surface of Mars to reach the ground?
Mars has a small moon, Phobos, that orbits with a period of 7 h 39 min. The radius of Phobos' orbit is 9.4 x 106 m. Use only this information (and the value of G) to calculate the mass of Mars.
Europa, a satellite of Jupiter, is believed to have a liquid ocean of water (with a possibility of life) beneath its icy surface. In planning a future mission to Europa, what is the fastest that an astronaut with legs of length 0.70 m could walk on the surface of Europa? Europa is 3100 km in
In Problems 70 through 73 you are given the equation (or equations) used to solve a problem. For each of these, you are toa. Write a realistic problem for which this is the correct equation. The last two questions should involve real planets. Be sure that the answer your problem requests is
In Problems 70 through 73 you are given the equation (or equations) used to solve a problem. For each of these, you are toa. Write a realistic problem for which this is the correct equation. The last two questions should involve real planets. Be sure that the answer your problem requests is
The 2.0 kg, uniform, horizontal rod in Figure P7.19 is seen from the side. What is the gravitational torque about the point shown? 25 cm FIGURE 75 cm P7.19
The 2.0-m-long, 15 kg beam in Figure P7.22 is hinged at its left end. It is "falling" (rotating clock- wise, under the influence of gravity), and the figure shows its position at three different times. What is the gravitational torque on the beam about an axis through the hinged end when the beam
As divers stand on tiptoes on the edge of a diving platform, in preparation for a high dive, as shown in Figure Q8.5, they usually extend their arms in front of them. Why do they do this? FIGURE Q8.5
A spring is attached to the floor and pulled straight up by a string. The string's tension is measured. The graph in Figure Q8.10 shows the tension in the spring as a function of the spring's length L.a. Does this spring obey Hooke's law? Explain. b. If it does, what is the spring constant? FIGURE
A spring exerts a 10 N force after being stretched by 1 cm from its equilibrium length. By how much will the spring force increase if the spring is stretched from 4 cm away from equilibrium to 5 cm from equilibrium?
You must lean quite far forward as you rise from a chair (try it!). Explain why.
How much torque must the pin exert to keep the rod in Figure P8.6 from rotating? Calculate this torque about an axis that passes through the point where the pin enters the rod and is perpendicular to the plane of the figure. Pin 80 cm 2.0 kg FIGURE P8.6 500 g
Where are the centers of gravity of the two people doing the classic yoga poses shown in Figure Q8.6? (a) FIGURE Q8.6 (b)
Take a spring and cut it in half to make two springs. Is the spring constant of these smaller springs larger, smaller, or the same as the spring constant of the original spring? Explain.
Steel nails are rigid and unbending. Steel wool is soft and squishy. How would you account for this difference?
A magazine rack has a center of gravity 16 cm above the floor, as shown in Figure P8.13. Through what maximum angle, in degrees, can the rack be tilted without falling over? 16 cm 5.0 cm FIGURE P8.13 End view
Two children carry a lightweight 1.8-m-long horizontal pole with a water bucket hanging from it. The older child supports twice as much weight as the younger child. How far is the bucket from the older child? A. 0.3 m B. 0.6 m C. 0.9 m D. 1.2 m
A car manufacturer claims that you can drive its new vehicle across a hill with a 47° slope before the vehicle starts to tip. If the vehicle is 2.0 m wide, how high is its center of gravity?
The uniform rod in Figure Q8.15 has a weight of 14.0 N. What is the magnitude of the normal force exerted on the rod by the surface?A. 7 N B. 14 N C. 20 N D. 28 N Frictionless surface FIGURE Q8.15
A thin 2.00 kg box rests on a 6.00 kg board that hangs over the end of a table, as shown in Figure P8.15. How far can the center of the box be from the end of the table before the board begins to tilt? 30.0 cm FIGURE P8.15 20.0 cm
A student lies on a very light, rigid board with a scale under each end. Her feet are directly over one scale, and her body is positioned as shown in Figure Q8.16. The two scales read the values shown in the figure. What is the student's weight? A. 65 lb B. 75 lb C. 100 lbD. 165 lb 65 lb FIGURE
The object shown in Figure P8.16 is made of a uniform material. What is the greatest that x can be without the object tipping over? 4.0 cm 2.0 cm FIGURE P8.16 2.0 cm
For the student in Figure Q8.16, approximately how far from her feet is her center of gravity?A. 0.6 m B. 0.8 m C. 1.0 m D. 1.2 m 65 lb FIGURE Q8.16 2.0 m 100 lb
One end of a spring is attached to a wall. A 25 N pull on the other end causes the spring to stretch by 3.0 cm. What is the spring constant?
You have a heavy piece of equipment hanging from a 1.0-mm- diameter wire. Your supervisor asks that the length of the wire be doubled without changing how far the wire stretches. What diameter must the new wire have? A. 1.0 mm B. 1.4 mm C. 2.0 mm D. 4.0 mm
A 30.0-cm-long board is placed on a table such that its right end hangs over the edge by 8.0 cm. A second identical board is stacked on top of the first, as shown in Figure Q8.22. What is the largest that the distance x can be before both boards topple over? A. 4.0 cm B. 8.0 cmC. 14 cmD. 15 cm
A 1.2 kg block is hung from a vertical spring, causing the spring to stretch by 2.4 cm. How much farther will the spring stretch if a 0.60 kg block is added to the 1.2 kg block?
Two 20 kg blocks are connected by a 2.0-m-long, 5.0-mm- diameter rope. Young's modulus for this rope is 1.5 X 109 N/m2. The rope is then hung over a pulley, so that the blocks, hanging from each side of the pulley, are in static equilibrium. By how much does the rope stretch?A. 3.0 mm B. 6.3 mmC.
A runner wearing spiked shoes pulls a 20 kg sled across frictionless ice using a horizontal spring with spring constant 1.5 X 102 N/m. The spring is stretched 20 cm from its equilibrium length. What is the acceleration of the sled?
You need to make a spring scale to measure the mass of objects hung from it. You want each 1.0 cm length along the scale to correspond to a mass difference of 0.10 kg. What should be the value of the spring constant?
A force stretches a wire by 1.0 mm. a. A second wire of the same material has the same cross section and twice the length. How far will it be stretched by the same force? b. A third wire of the same material has the same length and twice the diameter as the first. How far will it be stretched by
What hanging mass will stretch a 2.0-m-long, 0.50-mm- diameter steel wire by 1.0 mm?
How much force does it take to stretch a 10-m-long, 1.0-cm- diameter steel cable by 5.0 mm?
A 1.2-m-long steel rod with a diameter of 0.50 cm hangs vertically from the ceiling. An auto engine weighing 4.7 kN is hung from the rod. By how much does the rod stretch?
A mine shaft has an elevator hung from a single steel-wire cable of diameter 2.5 cm. When the cable is fully extended, the end of the cable is 500 m below the support. How much does the fully extended cable stretch when 3000 kg of ore is loaded into the elevator?
The normal force of the ground on the foot can reach three times a runner's body weight when the foot strikes the pavement. By what amount does the 52-cm-long femur of an 80 kg runner compress at this moment? The cross-section area of the bone of the femur can be taken as 5.2 × 10-4 m2.
An 80 kg construction worker sits down 2.0 m from the end of a 1450 kg steel beam to eat his lunch, as shown in Figure P8.36. The cable supporting the beam is rated at 15,000 N. Should the worker be worried? FIGURE P8.36 6.0 m Cable 30%
A woman weighing 580 N does a pushup from her knees, as shown in Figure P8.38. What are the normal forces of the floor on.(a) Each of her hands (b) Each of her knees? 54 cm 76 cm FIGURE P8.38
A man is attempting to raise a 7.5-m-long, 28 kg. flagpole that has a hinge at the base by pulling on a rope attached to the top of the pole, as shown in Figure P8.41. With what force does the man have to pull on the rope to hold the pole motionless in this position? FIGURE P8.41 20° 30° 7.5 m
A "rocket car" is launched along a long straight track at t = 0 s. It moves with constant acceleration a1 = 2.0 m/s2. At t = 2.0 s, a second car is launched along a parallel track, from the same starting point, with constant acceleration a2 = 8.0 m/s2. a. At what time does the second car catch up
If an astronaut can jump straight up to a height of 0.50 m on earth, how high could he jump on the moon?A. 1.2 m B. 3.0 m C. 3.6 m D. 18 m
On the earth, an astronaut can safely jump to the ground from a height of 1.0 m; her velocity when reaching the ground is slow enough to not cause injury. From what height could the astronaut safely jump to the ground on the moon? A. 2.4 m B. 6.0 m C. 7.2 m D. 36 m
On the earth, an astronaut throws a ball straight upward; it stays in the air for a total time of 3.0 s before reaching the ground again. If a ball were to be thrown upward with the same initial speed on the moon, how much time would pass before it hit the ground? A. 7.3 s B. 18 s C. 44 s D.
a. Can a vector have nonzero magnitude if a component is zero? If no, why not? If yes, give an example. b. Can a vector have zero magnitude and a nonzero component? If no, why not? If yes, give an example.
A car goes around a corner in a circular are at constant speed. Draw a motion diagram including positions, velocity vectors, and acceleration vectors.
a. Is the object's average speed between points 1 and 2 greater than, less than, or equal to its average speed between points 0 and 1? Explain how you can tell. b. Find the average acceleration vector at point 1 of the three-point motion diagram in Figure P3.4.Figure P3.4. 1. 0 20 FIGURE P3.4
Figure 3.11 showed the motion diagram for Anne as she rode a Ferris wheel that was turning at a constant speed. The inset to the figure showed how to find the acceleration vector at the lowest point in her motion. Use a similar analysis to find Anne's acceleration vector at the 12 o'clock, 4
A position vector with magnitude 10 m points to the right and up. Its x-component is 6.0 m. What is the value of its y-component?
An athlete performing the long jump tries to achieve the maximum distance from the point of takeoff to the first point of touching the ground. After the jump, rather than land upright, she extends her legs forward as in the photo. How does this affect the time in the air? How does this give the
A person trying to throw a ball as far as possible will run forward during the throw. Explain why this increases the distance of the throw.
A passenger on a jet airplane claims to be able to walk at a speed in excess of 500 mph. Can this be true? Explain.
If you go to a ski area, you'll likely find that the beginner's slope has the smallest angle. Use the concept of acceleration on a ramp to explain why this is so.
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