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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

Draw each of the following vectors, then find its x- and y-components. à a. b. c. à = (100 m, 45° below +x-axis) (300 m/s, 20° above +x-axis) (5.0 m/s², -y-direction)
In an amusement-park ride, cars rolling along at high speed suddenly head up a long, straight ramp. They roll up the ramp. reverse direction at the highest point, then roll backward back down the ramp. In each of the following segments of the motion, are the cars accelerating, or is their
There are competitions in which pilots fly small planes low over the ground and drop weights, trying to hit a target. A pilot flying low and slow drops a weight; it takes 2.0 s to hit the ground, during which it travels a horizontal distance of 100 m. Now the pilot does a run at the same height but
Draw each of the following vectors, then find its x- and y-components. d = (2.0 km, 30° left of +y-axis) (5.0 cm/s, -x-direction) (10 m/s², 40° left of -y-axis) a. b. c. à
Each of the following vectors is given in terms of its x- and y-components. Draw the vector, label an angle that specifies the vector's direction, then find the vector's magnitude and direction. a. v, 20 m/s, v, = 40 m/s b. a 2.0 m/s², a, = -6.0 m/s² =
A cyclist goes around a level, circular track at constant speed. Do you agree or disagree with the following statement: "Because the cyclist's speed is constant, her acceleration is zero." Explain.
Each of the following vectors is given in terms of its x- and y-components. Draw the vector, label an angle that specifies the vector's direction, then find the vector's magnitude and direction. a. v, 10 m/s, v, = 30 m/s = b. a, 20 m/s², a, = 10 m/s²
You are driving your car in a circular path on level ground at a constant speed of 20 mph. At the instant you are driving north, and turning left, are you accelerating? If so, toward what point of the compass (N, S, E, W) does your acceleration vector point? If not, why not?
While visiting England, you decide to take a jog and find yourself in the neighborhood shown on the map in Figure P3.15. What is your displacement after running 2.0 km on Strawberry Fields, 1.0 km on Penny Lane, and 4.0 km on Abbey Road? Start FIGURE P3.15 Strawberry Fields Penny Lane 40° Abbey
An airplane has been directed to fly in a clockwise circle, as seen from above, at constant speed until another plane has landed. When the plane is going north, is it accelerating? If so, in what direction does the acceleration vector point? If not, why not?
When you go around a corner in your car, your car follows a path that is a segment of a circle. To turn safely, you should keep your car's acceleration below some safe upper limit. If you want to make a "tighter" turn-that is, turn in a circle with a smaller radius-how should you adjust your speed?
Which combination of the vectors shown in Figure Q3.17 has the largest magnitude? A TR0 B FIGURE Q3.17 Ĉ
You begin sliding down a 15° ski slope. Ignoring friction and air resistance, how fast will you be moving after 10 s?
Two vectors appear as in Figure Q3.18. Which combination points directly to the left? TA FIGURE Q3.18 ē
A car traveling at 30 m/s runs out of gas while traveling up a 5.0° slope. How far will it coast before starting to roll back down?
In the Soapbox Derby, young participants build nonmotorized cars with very low friction wheels. Cars race by rolling down a hill. The track at Akron's Derby Downs, where the national championship is held, begins with a 55- ft ~long section tilted 13° below horizontal.a. What is the maximum
The gas pedal in a car is sometimes referred to as "the accelerator." Which other controls on the vehicle can be used to produce acceleration? A. The brakes. B. The steering wheel. C. The gear shift. D. All of the above.
Two children who are bored while waiting for their flight at the airport decide to race from one end of the 20-m-long moving sidewalk to the other and back. Phillippe runs on the side- walk at 2.0 m/s (relative to the sidewalk). Renee runs on the floor at 2.0 m/s. The sidewalk moves at 1.5 m/s
A skydiver deploys his parachute when he is 1000 m directly above his desired landing spot. He then falls through the air at a steady 5.0 m/s. There is a breeze blowing to the west at 2.0 m/s. a. At what angle with respect to vertical does he fall? b. By what distance will he miss his desired
A football is kicked at an angle of 30° with a speed of 20 m/s. To the nearest second, how long will the ball stay in the air? A. 1 s B. 2 s C. 3 sD. 4 s
A football is kicked at an angle of 30° with a speed of 20 m/s. To the nearest 5 m, how far will the ball travel? A. 15 m B. 25 m C. 35 m D. 45 m
A ball is thrown horizontally from a 20-m-high building with a speed of 5.0 m/s.a. Make a sketch of the ball's trajectory. b. Draw a graph of vy, the horizontal velocity, as a function of time. Include units on both axes. c. Draw a graph of vy, the vertical velocity, as a function of time.
Riders on a Ferris wheel move in a circle with a speed of 4.0 m/s. As they go around, they experience a centripetal acceleration of 2.0 m/s. What is the diameter of this particular Ferris wheel? A. 4.0 m B. 6.0 m C. 8.0 mD. 16 mE. 24 m
A ball with a horizontal speed of 1.25 m/s rolls off a bench 1.00 m above the floor. a. How long will it take the ball to hit the floor? b. How far from a point on the floor directly below the edge of the bench will the ball land?
King Arthur's knights use a catapult to launch a rock from their vantage point on top of the castle wall, 12 m above the moat. The rock is launched at a speed of 25 m/s and an angle of 30 above the horizontal. How far from the castle wall does the launched rock hit the ground?
Two spheres are launched horizontally from a 1.0-m-high table. Sphere A is launched with an initial speed of 5.0 m/s. Sphere B is launched with an initial speed of 2.5 m/s. a. What are the times for each sphere to hit the floor? b. What are the distances that each travels from the edge of the
Racing greyhounds are capable of rounding corners at very high speeds. A typical greyhound track has turns that are 45-m- diameter semicircles. A greyhound can run around these turns at a constant speed of 15 m/s. What is its acceleration in m/s and in units of g?
A CD-ROM drive in a computer spins the 12-cm-diameter disks at 10,000 rpm. a. What are the disk's period (in s) and frequency (in rev/s)? b. What would be the speed of a speck of dust on the outside edge of this disk? c. What is the acceleration in units of g that this speck of dust experiences?
Entrance and exit ramps for freeways are often circular stretches of road. As you go around one at a constant speed, you will experience a constant acceleration. Suppose you drive through an entrance ramp at a modest speed and your acceleration is 3.0 m/s2. What will be the acceleration if you
A typical set of stairs is angled at 38°. You climb a set of stairs at a speed of 3.5 m/s. a. How much height will you gain in 2.0 s? b. How much horizontal distance will you cover in 2.0 s?
A pilot in a small plane encounters shifting winds. He flies 26.0 km northeast, then 45.0 km due north. From this point, he flies an additional distance in an unknown direction, only to find himself at a small airstrip that his map shows to be 70.0 km directly north of his starting point. What were
A small plane is 100 km south of the equator. The plane is flying at 150 km/h at a heading of 30 to the west of north. In how many minutes will the plane cross the equator?
A block slides along the frictionless track shown in Figure P3.54 with an initial speed of 5.0 m/s. Assume it turns all the corners smoothly, with no loss of speed.a. What is the block's speed as it goes over the top? b. What is its speed when it reaches the level track on the right side? c. By
When the moving sidewalk at the airport is broken, as it often seems to be, it takes you 50 s to walk from your gate to the bag- gage claim. When it is working and you stand on the moving side- walk the entire way, without walking, it takes 75 s to travel the same distance. How long will it take
Mary needs to row her boat across a 100-m-wide river that is flowing to the east at a speed of 1.0 m/s. Mary can row the boat with a speed of 2.0 m/s relative to the water. a. If Mary rows straight north, how far downstream will she land? b. Draw a picture showing Mary's displacement due to
A flock of ducks is trying to migrate south for the winter, but they keep being blown off course by a wind blowing from the west at 12 m/s. A wise elder duck finally realizes that the solution is to fly at an angle to the wind. If the ducks can fly at 16 m/s relative to the air, in what direction
A 1500 kg car is traveling along a straight road at 20 m/s. Two seconds later its speed is 21 m/s. What is the magnitude of the net force acting on the car during this time?
Tennis balls experience a large drag force. A tennis ball is hit so that it goes straight up and then comes back down. The direction of the drag force is. A. Always up. B. Up and then down. C. Always down. D. Down and then up.
Very small forces can have tremendous effects on the motion of very small objects. Consider a single electron, with a mass of 9.1 x 10-31 kg, subject to a single force equal to the weight of a penny, 2.5 X 10-2 N. What is the acceleration of the electron?
The Gulf Stream off the east coast of the United States can flow at a rapid 3.6 m/s to the north. A ship in this current has a cruising speed of 10 m/s. The captain would like to reach land at a point due west from the current position. a. In what direction with respect to the water should the
A spring-loaded gun, fired vertically, shoots a marble 6.0 m straight up in the air. What is the marble's range if it is fired horizontally from 1.5 m above the ground?
A mountain climber is hanging from a rope in the middle of a crevasse. The rope is vertical. Identify the forces on the mountain climber.
In a shot-put event, an athlete throws the shot with an initial speed of 12.0 m/s at a 40.0° angle from the horizontal. The shot leaves her hand at a height of 1.80 m above the ground. a. How far does the shot travel? b. Repeat the calculation of part (a) for angles 42.5°, 45.0°, and 47.5°.
Water at the top of Horseshoe Falls (part of Niagara Falls) is moving horizontally at 9.0 m/s as it goes off the edge and plunges 53 m to the pool below. If you ignore air resistance, at what angle is the falling water moving as it enters the pool?
Suppose the designers of the water slide want to adjust the height h above the water so that riders land twice as far away from the bottom of the slide. What would be the necessary height above the water? A. 1.2 m B. 1.8 m C. 2.4 m D. 3.0 m
Whiplash injuries during an automobile accident are caused by the inertia of the head. If someone is wearing a seatbelt, her body will tend to move with the car seat. However, her head is free to move until the neck restrains it, causing damage to the neck. Brain damage can also occur. Figure P4.1
During which section of the motion is the magnitude of the acceleration experienced by a rider the greatest? A. The first. B. The second. C. The third. D. It is the same in all sections.
A hockey puck slides along the surface of the ice. If friction and air resistance are negligible, what force is required to keep the puck moving?
An automobile has a head-on collision. A passenger in the car experiences a compression injury to the brain. Is this injury most likely to be in the front or rear portion of the brain? Explain.
If an object is not moving, does that mean that there are no forces acting on it? Explain.
In a head-on collision, an infant is much safer in a child safety seat when the seat is installed facing the rear of the car. Explain.
An object moves in a straight line at a constant speed. Is it true that there must be no forces of any kind acting on this object? Explain.
Three arrows are shot horizontally. They have left the bow and are traveling parallel to the ground as shown in Figure Q4.6. Air resistance is negligible. Rank in order, from largest to smallest, the magnitudes of the horizontal forces F1, F2, and F3 acting on the arrows. Some may be equal. State
A ball sits near the front of a child's wagon. As she pulls on the wagon and it begins to move forward, the ball rolls toward the back of the wagon. Explain why the ball rolls in this direction.
A carpenter wishes to tighten the heavy head of his hammer onto its light handle. Which method shown in Figure Q4.7 will better tighten the head? Explain. FIGURE Q4.7
A circus clown hangs from one end of a large spring. The other end is anchored to the ceiling. Identify the forces on the clown.
Internal injuries in vehicular accidents may be due to what is called the "third collision." The first collision is the vehicle hitting the external object. The second collision is the person hitting something on the inside of the car, such as the dashboard or windshield. This may cause external
a. Give an example of the motion of an object in which the frictional force on the object is directed opposite to the motion. b. Give an example of the motion of an object in which the frictional force on the object is in the same direction as the motion.
Suppose you are an astronaut in deep space, far from any source of gravity. You have two objects that look identical, but one has a large mass and the other a small mass. How can you tell the difference between the two?
Jonathan accelerates away from a stop sign. His eight-year-old daughter sits in the passenger seat. On whom does the back of the seat exert a greater force?
A skier is sliding down a 15° slope. Friction is not negligible. Identify the forces on the skier.
The weight of a box sitting on the floor points directly down. The normal force of the floor on the box points directly up. Need these two forces have the same magnitude? Explain.
A tennis ball is flying horizontally across the net. Air resistance is not negligible. Identify the forces on the ball.
A ball weighs 2.0 N when placed on a scale. It is then thrown straight up. What is its weight at the very top of its motion? Explain.
Josh and Taylor, standing face-to-face on frictionless ice, push off each other, causing each to slide backward. Josh is much bigger than Taylor. After the push, which of the two is moving faster?
A person sits on a sloped hillside. Is it ever possible to have the static friction force on this person point down the hill? Explain.
Walking without slipping requires a static friction force between your feet (or footwear) and the floor. As described in this chapter, the force on your foot as you push off the floor is forward while the force exerted by your foot on the floor is backward. But what about your other foot, the one
Figure P4.21 shows an object's acceleration-versus-force graph. What is the object's mass? a (m/s²) 4 لیا 2 1 0 FIGURE P4.21 0.0 0.5 1.0 - F (N)
A car has a maximum acceleration of 5.0 m/s2. What will the maximum acceleration be if the car is towing another car of the same mass?
A block has acceleration a when pulled by a string. If two identical blocks are glued together and pulled with twice the original force, their acceleration will be A. (1/4)a B. (1/2)a C. a D. 2aE. 4a
Two children fight over a 200 g stuffed bear. The 25 kg boy pulls to the right with a 15 N force and the 20 kg girl pulls to the left with a 17 N force. Ignore all other forces on the bear (such as its weight). a. At this instant, can you say what the velocity of the bear is? If so, what are the
A 5.0 kg block has an acceleration of 0.20 m/s2 when a force is exerted on it. A second block has an acceleration of 0.10 m/s2 when subject to the same force. What is the mass of the second block?A. 10 kg B. 5.0 kg C. 2.5 kg D. 7.5 kg
A person gives a box a shove so that it slides up a ramp, then reverses its motion and slides down. The direction of the force of friction is A. Always down the ramp. B. Up the ramp and then down the ramp. C. Always down the ramp. D. Down the ramp and then up the ramp.
A person is pushing horizontally on a box with a constant force, causing it to slide across the floor with a constant speed. If the person suddenly stops pushing on the box, the box will.A. Immediately come to a stop. B. Continue moving at a constant speed for a while, then gradually slow down to
Rachel is pushing a box across the floor while Jon, at the same time, is hoping to stop the box by pushing in the opposite direction. There is friction between the box and floor. If the box is moving at constant speed, then the magnitude of Rachel's pushing force isA. Greater than the magnitude of
Dave pushes his four-year-old son Thomas across the snow on a sled. As Dave pushes, Thomas speeds up. Which statement is true? A. The force of Dave on Thomas is larger than the force of Thomas on Dave. B. The force of Thomas on Dave is larger than the force of Dave on Thomas. C. Both forces have
Three ice skaters, numbered 1, 2, and 3, stand in a line, each with her hands on the shoulders of the skater in front. Skater 3, at the rear, pushes on skater 2. Identify all the action/reaction pairs of forces between the three skaters. Draw a free- body diagram for skater 2, in the middle. Assume
Redraw the motion diagram shown in Figure P4.40, then draw a vector beside it to show the direction of the net force acting on the object. Explain your reasoning. FIGURE P4.40
A girl stands on a sofa. Identify all the action/reaction pairs of forces between the girl and the sofa.
A student draws the flawed free-body diagram shown in Figure P4.50 to represent the forces acting on a car traveling at constant speed on a level road. Identify the errors in the diagram, then draw a correct free-body diagram for this situation. Incorrect diagram! Action/
A student draws the flawed free-body diagram shown in Figure P4.51 to represent the forces acting on a golf ball that is traveling upward and to the right a very short time after being hit off the tee. Air resistance is assumed to be relevant. Identify the errors in the diagram, then draw a correct
A beach ball is thrown straight up, and some time later it lands on the sand. Is the magnitude of the net force on the ball greatest when it is going up or when it is on the way down? Or is it the same in both cases? Explain. Air resistance should not be neglected for a large, light object.
When you are pulling on the rope as shown, what is the approximate direction of the tension force on the tree? A. North B. South C. East D. West
Assume that you are pulling on the rope but the car is not moving. What is the approximate direction of the force of the mud on the car? A. North B. South C. East D. West
Suppose your efforts work, and the car begins to move for- ward out of the mud. As it does so, the force of the car on the rope is.A. Zero. B. Less than the force of the rope on the car. C. Equal to the force of the rope on the car. D. Greater than the force of the rope on the car.
An object is subject to two forces that do not point in opposite directions. Is it possible to choose their magnitudes so that the object is in equilibrium? Explain.
What forces are acting on you right now? What net force is acting on you right now?
A 1000 kg steel beam is supported by the two ropes shown in Figure P5.4. Each rope can support a maximum sustained tension of 5600 N. Do the ropes break? Rope 1- 30° 30° FIGURE P5.4 -Rope 2
A 20 kg loudspeaker is suspended 2.0 m below the ceiling by two cables that are each 30 from vertical. What is the tension in the cables?
A light block of mass m and a heavy block of mass M are attached to the ends of a rope. A student holds the heavier block and lets the lighter block hang below it, as shown in Figure Q5.6. Then she lets go. Air resistance can be neglected.a. What is the tension in the rope while the blocks are
When you bend your knee, the quadriceps muscle is stretched. This increases the tension in the quadriceps tendon attached to your knee cap (patella), which, which, in turn, increases the tension in the patella tendon that attaches your kneecap to your lower leg bone (tibia). Simultaneously, the end
The two angled ropes used to support the crate in Figure P5.7 can withstand a maximum tension of 1500 N before they break. What is the largest mass the ropes can support? 30° FIGURE P5.7 45°
Three objects move through the air as shown in Figure Q5.11. Rank in order, from largest to smallest, the three drag forces D1, D2, and D3. Some may be equal. Give your answer in the form A > B = C and state your reasoning.Figure Q5.11. 6 m/s 20 cm x 30 cm 2 6 m/s 20 cm x 20 cm 3 4 m/s 30 cm x
A ball is thrown straight up. Taking the drag force of air into account, does it take longer for the ball to travel to the top of its motion or for it to fall back down again?
A skydiver is falling at her terminal speed. Right after she opens her parachute, which has a very large area, what is the direction of the net force on her?
Raindrops can fall at different speeds; some fall quite quickly, others quite slowly. Why might this be true?
An airplane moves through the air at a constant speed. The jet engine's thrust applies a force in the direction of motion. Reducing thrust will cause the plane to fly at a slower-but still constant speed. Explain why this is so.
Is it possible for an object to travel in air faster than its terminal speed? If not, why not? If so, explain how this might happen.
For Questions determine the tension in the rope at the point indicated with a dot. • All objects are at rest. • The strings and pulleys are massless, and the pulleys are frictionless. 5 kg FIGURE Q5.16
In a head-on collision, a car stops in 0.10 s from a speed of 14 m/s. The driver has a mass of 70 kg, and is, fortunately, tightly strapped into his seat. What force is applied to the driver by his seat belt during that fraction of a second?

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