Questions and Answers of College Physics A Strategic Approach 2nd

A library ladder of length L rolls on wheels as shown in Figure P8.42. The two legs of the ladder freely pivot at the hinge at the top. The legs are kept from splaying apart by a light- weight chain
The wheel of mass m in Figure P8.44 is pulled on by a horizontal force applied at its center. The wheel is touching a curb whose height is half the wheel's radius. What is the minimum force required
A 40 kg, 5.0-m-long beam is supported by, but not attached to, the two posts in Figure P8.43. A 20 kg boy starts walking along the beam. How close can he get to the right end of the beam without it
Two springs have the same spring constant k = 130 N/m but different equilibrium lengths, 3.0 cm and 5.0 cm. They are arranged as shown in Figure P8.48, then a block is pushed against them,
Figure P8.49 shows two springs attached to a block that can slide on a friction less surface. In the block's equilibrium position, the left spring is compressed by 2.0 cm.a. By how much is the right
Figure P8.50 shows two springs attached to each other, and also attached to a box that can slide on a frictionless surface. In the block's equilibrium position, neither spring is stretched. What is
A 25 kg child bounces on a pogo stick. The pogo stick has a spring with spring constant 2.0 X 104 N/m. When the child makes a nice big bounce, she finds that at the bottom of the bounce she is
Orb spiders make silk with a typical diameter of 0.15 mm.a. A typical large orb spider has a mass of 0.50 g. If this spider suspends itself from a single 12-cm-long strand of silk, by how much will
A 57 g tennis ball is served at 45 m/s. If the ball started from rest, what impulse was applied to the ball by the racket?
Starting from rest, object 1 is subject to a 12 N force for 2.0 s. Object 2, with twice the mass, is subject to a 15 N force for 3.0 s. Which object has the greater final speed? Explain.
A student throws a 120 g snowball at 7.5 m/s at the side of the schoolhouse, where it hits and sticks. What is the magnitude of the average force on the wall if the duration of the collision is 0.15
Two pucks, of mass m and 4m, lie on a frictionless table. Equal forces are used to push both pucks forward a distance of 1 m. a. Which puck takes longer to travel the distance? Explain. b. Which
A stationary firecracker explodes into three pieces. One piece travels off to the east; a second travels to the north. Which of the vectors of Figure Q9.5 could be the velocity of the third piece?
A sled and rider, gliding over horizontal, frictionless ice at 4.0 m/s, have a combined mass of 80 kg. The sled then slides over a rough spot in the ice, slowing down to 3.0 m/s. What impulse was
Two students stand at rest, facing each other on frictionless skates. They then start tossing a heavy ball back and forth between them. Describe their subsequent motion.
Automobiles are designed with "crumple zones" intended to collapse in a collision. Why would a manufacturer design part of a car so that it collapses in a collision?
A child is sliding on a sled at 1.5 m/s to the right. You stop the sled by pushing on it for 0.50 s in a direction opposite to its motion. If the mass of the child and sled is 35 kg, what average
You probably know that it feels better to catch a baseball if you are wearing a padded glove. Explain why this is so, using the ideas of momentum and impulse.
An ice hockey puck slides along the ice at 12 m/s. A hockey stick delivers an impulse of 4.0 kg • m/s, causing the puck to move off in the opposite direction with the same speed. What is the mass
In the early days of rocketry, some people claimed that rockets couldn't fly in outer space as there was no air for the rockets to push against. Suppose you were an early investigator in the field of
As part of a safety investigation, two 1400 kg cars traveling at 20 m/s are crashed into different barriers. Find the average forces exerted on (a). The car that hits a line of water barrels and
Two ice skaters, Megan and Jason, push off from each other on frictionless ice. Jason's mass is twice that of Megan. a. Which skater, if either, experiences the greater impulse during the push?
In a Little League baseball game, the 145 g ball enters the strike zone with a speed of 15.0 m/s. The batter hits the ball, and it leaves his bat with a speed of 20.0 m/s in exactly the opposite
Suppose a rubber ball and a steel ball collide. Which, if either, receives the larger impulse? Explain.
A small, 100 g cart is moving at 1.20 m/s on an air track when it collides with a larger, 1.00 kg cart at rest. After the collision, the small cart recoils at 0.850 m/s. What is the speed of the
While standing still on a basketball court, you throw the ball to a teammate. Why do you not move backward as a result? Is the law of conservation of momentum violated?
A man standing on very slick ice fires a rifle horizontally. The mass of the man together with the rifle is 70 kg, and the mass of the bullet is 10 g. If the bullet leaves the muzzle at a speed of
Rank in order, from largest to smallest, the angular momenta L1 through L5, of the balls shown in Figure Q9.15. Explain. 3 m/s 2 m/s [ m/s 2 kg 3 kg බිමට 2m 2 m 2 m 2 1 FIGURE 09.15 3 1 kg 2
To win a prize at the county fair, you're trying to knock down a heavy bowling pin by hitting it with a thrown object. Should you choose to throw a rubber ball or a beanbag of equal size and weight?
A 2.7 kg block of wood sits on a table. A 3.0 g bullet, fired horizontally at a speed of 500 m/s, goes completely through the block, emerging at a speed of 220 m/s. What is the speed of the block
Figure Q9.16 shows two masses held together by a thread on a rod that is rotating about its center with angular velocity w. If the thread breaks, the masses will slide out to the ends of the rod. If
A strong man is compressing a lightweight spring between two weights. One weight has a mass of 2.3 kg, the other a mass of 5.3 kg. He is holding the weights stationary, but then he loses his grip and
If the earth warms significantly, the polar ice caps will melt. Water will move from the poles, near the earth's rotation axis. and will spread out around the globe. In principle, this will change
Two balls are hung from cords. The first ball, of mass 1.0 kg, is pulled to the side and released, reaching a speed of 2.0 m/s at the bottom of its arc. Then, as shown in Figure Q9.20, it hits and
Curling is a sport played with 20 kg stones that slide across an ice surface. Suppose a curling stone sliding at 1 m/s strikes another stone and comes to rest in 2 ms. Approximately how much force is
Two friends are sitting in a stationary canoe. At t = 3.0 s the person at the front tosses a sack to the person in the rear, who catches the sack 0.2 s later. Which plot in Figure Q9.22 shows the
A 9.5 kg dog takes a nap in a canoe and wakes up to find the canoe has drifted out onto the lake but now is stationary. He walks along the length of the canoe at 0.50 m/s, relative to the water, and
A 71 kg baseball player jumps straight up to catch a line drive. If the 140 g ball is moving horizontally at 28 m/s, and the catch is made when the ballplayer is at the highest point of his leap,
Two blocks, with masses m1 = 2.5 kg and m2 = 14 kg, approach each other along a horizontal, frictionless track. The initial velocities of the blocks are v1 = 12.0 m/s to the right and v2 = 3.4 m/s to
A kid at the junior high cafeteria wants to propel an empty milk carton along a lunch table by hitting it with a 3.0 g spit ball. If he wants the speed of the 20 g carton just after the spit ball
A red ball, initially at rest, is simultaneously hit by a blue ball traveling from west to east at 3 m/s and a green ball traveling east to west at 3 m/s. All three balls have equal mass. Afterward,
A 2.0 kg block slides along a frictionless surface at 1.0 m/s. A second block, sliding at a faster 4.0 m/s, collides with the first from behind and sticks to it. The final velocity of the combined
A 24 g, 3-cm-diameter thin, hollow sphere rotates at 30 rpm about a vertical, frictionless axis through its center. A 4 g bug stands at the top of the sphere. He then walks along the surface of the
Il Two particles collide and bounce apart. Figure P9.27 shows the initial momenta of both and the final momentum of particle 2. What is the final momentum of particle 1? Show your answer by copying
What is the angular momentum of the moon around the earth? The moon's mass is 7.4 x 1022 kg and it orbits 3.8 x 108 m from the earth.
A little girl is going on the merry-go-round for the first time, and wants her 47 kg mother to stand next to her on the ride, 2.6 m from the merry-go-round's center. If her mother's speed is 4.2 m/s
What is the angular momentum about the axle of the 500 g rotating bar in Figure P9.32? 2.0 m FIGURE P9.32 120 rpm Axle
Divers change their body position in midair while rotating about their center of mass. In one dive, the diver leaves the board with her body nearly straight, then tucks into a somersault position. If
A 200 g ball is dropped from a height of 2.0 m and bounces on a hard floor. The force on the ball from the floor is shown in Figure P9.40. How high does the ball rebound? F (N) 1000 앙 FIGURE
Figure P9.41 is a graph of the force exerted by the floor on a woman making a vertical jump. At what speed does she leave the ground? F, (N) 2400- 1800 1200 600 0- 0 0.2 FIGURE P9.41 0.4 0.6 t(s)
A 140 g baseball is moving horizontally to the right at 35 m/s when it is hit by the bat. The ball flies off to the left at 55 m/s, at an angle of 25° above the horizontal. What are the magnitude
Squids rely on jet propulsion, a versatile technique to move around in water. A 1.5 kg squid at rest suddenly expels 0.10 kg of water backward to quickly get itself moving forward at 3.0 m/s. If
James and Sarah stand on a stationary cart with frictionless wheels. The total mass of the cart and riders is 130 kg. At the same instant, James throws a 1.0 kg ball to Sarah at 4.5 m/s, while Sarah
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
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
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
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
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
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
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
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
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
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
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
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.
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
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
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
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
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
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.
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
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
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
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
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
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
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
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
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?
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
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
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
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

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