Questions and Answers of College Physics A Strategic Approach 2nd

The fastest recorded skydive was by an Air Force officer who jumped from a helium balloon at an elevation of 103,000 ft, three times higher than airliners fly. Because the density of air is so low at
Two blocks are connected by a string as in Figure P5.70. What is the upper block's acceleration if the coefficient of kinetic friction between the block and the table is 0.20? 2.0 kg Pulley FIGURE
A 2.7 g Ping-Pong ball has a diameter of 4.0 cm. a. The ball is shot straight up at twice its terminal speed. What is its initial acceleration? b. The ball is shot straight down at twice its
The 10 kg block in Figure P5.71 slides down a frictionless ramp. What is its acceleration? 10 kg 40° FIGURE P5.71 5.0 kg
A 2.0 kg wood block is pulled along a wood floor at a steady speed. A second wood block, with mass 3.0 kg, is attached to the first by a horizontal string. What is the magnitude of the force pulling
A magician pulls a tablecloth out from under some dishes. How far do the dishes move during the 0.25 s it takes to pull out the tablecloth? The coefficient of kinetic friction between the cloth and
A curler pushes a stone to a speed of 3.0 m/s over a time of 2.0 s. Ignoring the force of friction, how much force must the curler apply to the stone to bring it up to speed? A. 3.0 N.B. 15 N C. 30
The sweepers in a curling competition adjust the trajectory of the stone by.A. Decreasing the coefficient of friction between the stone and the ice. B. Increasing the coefficient of friction between
Suppose the stone is launched with a speed of 3 m/s and travels 40 m before coming to rest. What is the approximate magnitude of the friction force on the stone? A. ON B. 2N C. 20 N D. 200 N
Suppose the stone's mass is increased to 40 kg, but it is launched at the same 3 m/s. Which one of the following is true? A. The stone would now travel a longer distance before coming to rest. B.
What is the angular position in radians of the minute hand of a clock at. (a) 5:00, (b) 7:15,(c) 3:35?
The batter in a baseball game hits a home run. As he circles the bases, is his angular velocity positive or negative?
A child on a merry-go-round takes 3.0 s to go around once. What is his angular displacement during a 1.0 s time interval?
Viewed from somewhere in space above the north pole, would a point on the earth's equator have a positive or negative angular velocity due to the earth's rotation?
What is the angular speed of the tip of the minute hand on a clock, in rad/s?
A cyclist goes around a level, circular track at constant speed. Do you agree or disagree with the following statement? "Since the cyclist's speed is constant, her acceleration is zero." Explain.
An old-fashioned vinyl record rotates on a turntable at 45 rpm. What are (a) the angular speed in rad/s and (b) the period of the motion?
A particle moving along a straight line can have nonzero acceleration even when its speed is zero (for instance, a ball in free fall at the top of its path). Can a particle moving in a circle have
A Ferris wheel rotates at an angular velocity of 0.036 rad/s. At t = 0 min, your friend Seth is at the very top of the ride. What is Seth's angular position at t = 3.0 min, measured counterclockwise
Would having four-wheel drive on a car make it possible to drive faster around corners on an icy road, without slipping, than the same car with two-wheel drive? Explain.
A turntable rotates counterclockwise at 78 rpm. A speck of dust on the turntable is at 0 = 0.45 rad at t = 0 s. What is the angle of the speck at 1 = 8.0 s? Your answer should be between 0 and 2π
Large birds like pheasants often walk short distances. Small birds like chickadees never walk. They either hop or fly. Why might this be?
A fast-moving superhero in a comic book runs around a circular, 70-m-diameter track five and a half times (ending up directly opposite her starting point) in 3.0 s. What is her angular speed, in
Figure P6.9 shows the angular position of a potter's wheel.a. What is the angular displacement of the wheel between t = 5 s and t = 15 s?b. What is the angular velocity of the wheel at t = 15 s?
When you drive fast on the highway with muddy tires, you can hear the mud flying off the tires into your wheel wells. Why does the mud fly off?
A ball on a string moves in a vertical circle as in Figure Q6.9. When the ball is at its lowest point, is the tension in the string greater than, less than, or equal to the ball's weight? Explain.
The angular velocity (in rpm) of the blade of a blender is given in Figure P6.10.a. If θ = 0 rad at t = 0 s, what is the blade's angular position at t = 20 s? b. At what time has the blade
Give an everyday example of circular motion for which the centripetal acceleration is mostly or completely due to a force of the type specified: (a) Static friction. (b) Tension.
Give an everyday example of circular motion for which the centripetal acceleration is mostly or completely due to a force of the type specified: (a) Gravity. (b) Normal force.
The blade on a table saw spins at 3450 rpm. Its diameter is 25.0 cm. What is the speed of a tooth on the edge of the blade, in both m/s and mph?
It's been proposed that future space stations create "artificial gravity" by rotating around an axis. (The space station would have to be much larger than the present space station for this to be
The horse on a carousel is 4.0 m from the central axis. a. If the carousel rotates at 0.10 rev/s, how long does it take the horse to go around twice? b. How fast is a child on the horse going (in
Why is it impossible for an astronaut inside an orbiting space shuttle to go from one end to the other by walking normally?
If every object in the universe feels an attractive gravitational force due to every other object, why don't you feel a pull from someone seated next to you?
A fast pitch softball player does a "windmill" pitch, illustrated in Figure P6.20, moving her hand through a circular arc to pitch a ball at 70 mph. The 0.19 kg ball is 50 cm from the pivot point at
A mountain climber's weight is less on the top of a tall mountain than at the base, though his mass is the same. Why?
Is the earth's gravitational force on the sun larger, smaller, or equal to the sun's gravitational force on the earth? Explain.
A baseball pitching machine works by rotating a light and stiff rigid rod about a horizontal axis until the ball is moving toward the target. Suppose a 144 g baseball is held 85 cm from the axis of
A ball on a string moves around a complete circle, once a second, on a frictionless, horizontal table. The tension in the string is measured to be 6.0 N. What would the tension be if the ball went
As seen from above, a car rounds the curved path shown in Figure Q6.22 at a constant speed. Which vector best represents the net force acting on the car?Figure Q6.22 B E D
You're driving your pickup truck around a curve with a radius of 20 m. A box in the back of the truck is pressed up against the wall of the truck. How fast must you drive so that the force of the
The cylindrical space station in Figure Q6.24, 200 m in diameter, rotates in order to provide artificial gravity of g for the occupants. How much time does the station take to complete one
You hold a bucket in one hand. In the bucket is a 500 g rock. You swing the bucket so the rock moves in a vertical circle 2.2 m in diameter. What is the minimum speed the rock must have at the top of
A newly discovered planet has twice the mass and three times the radius of the earth. What is the free-fall acceleration at its surface, in terms of the free-fall acceleration g at the surface of the
Two cylindrical space stations, the second four times the diameter of the first, rotate so as to provide the same amount of artificial gravity. If the first station makes one rotation in the time T,
Suppose one night the radius of the earth doubled but its mass stayed the same. What would be an approximate new value for the free-fall acceleration at the surface of the earth? A. 2.5 m/s² B. 5.0
What is the approximate angular speed of the skater during the leap?A. 2rad/s B. 6rad/s C. 9rad/s D. 20rad/s
The skater's arms are fully extended during the jump. What is the approximate centripetal acceleration of the skater's hand? A. 10 m/s2 B. 30 m/s2 C. 300 m/s2 D. 450 m/s2
What is the approximate speed of the skater's hand?A. 1 m/s B. 3 m/s C. 9 m/s D. 15 m/s
What is the free-fall acceleration at the surface of (a) Mars(b) Jupiter?
Satellite A orbits a planet with a speed of 10,000 m/s. Satellite B is twice as massive as satellite A and orbits at twice the distance from the center of the planet. What is the speed of satellite B?
A 30 g ball rolls around a 40-cmdiamete r L-shaped track, shown in Figure P6.47, at 60 rpm. Rolling friction can be neglected.a. How many different contact forces does the track exert on the ball?
The Space Shuttle is in a 250-mile-high orbit. What are the shuttle's orbital period, in minutes, and its speed?
A conical pendulum is formed by attaching a 500 g ball to a 1.0-m-long string, then allowing the mass to move in a horizontal circle of radius 20 cm. Figure P6.49 shows that the string traces out the
The 0.20 kg puck on the frictionless, horizontal table in Figure P6.51 is connected by a string through a hole in the table to a hanging 1.20 kg block. With what speed must the puck rotate in a
The Space Shuttle orbits 300 km above the surface of the earth. a. What is the force of gravity on a 1.0 kg sphere inside the Space Shuttle? b. The sphere floats around inside the Space Shuttle,
a. What is the free-fall acceleration on Mars? b. Estimate the maximum speed at which an astronaut can walk on the surface of Mars.
The material that comprises the side of the moon facing the earth is actually slightly more dense than the material on the far side. When the spacecraft is above a more dense area of the surface, the
To throw a discus, the thrower holds it with a fully outstretched arm. Starting from rest, he begins to turn with a constant angular acceleration, releasing the discus after making one complete
A computer hard disk starts from rest, then speeds up with an angular acceleration of 190 rad/s2 until it reaches its final angular speed of 7200 rpm. How many revolutions has the disk made 10.0 s
The crankshaft in a race car goes from rest to 3000 rpm in 2.0 s.a. What is the crankshaft's angular acceleration? b. How many revolutions does it make while reaching 3000 rpm?
What is the net torque of the bar shown in Figure P7.12, about the axis indicated by the dot? 25 cm FIGURE P7.12 75 cm 10 N 8.0 N
What is the net torque about the axle on the pulley in Figure P7.7? 20 N 4.0 cm FIGURE P7.7 30 N
Tom and Jerry both push on the 3.00-m-diameter merry-go round shown in Figure P7.11. Figure P7.11a. If Tom pushes with a force of 40.0 N and Jerry pushes with a force of 35.2 N, what is the net
What is the net torque of the bar shown in Figure P7.13, about the axis indicated by the dot? 8.0 N 25 cm FIGURE P7.13 75 cm 10 N
What is the net torque of the bar shown in Figure P7.14, about the axis indicated by the dot? FIGURE P7.14 8.0 N 40% 25 cm 75 cm 10 N, 30°
A 1.7-m-long barbell has a 20 kg weight on its left end and a 35 kg weight on its right end. a. If you ignore the weight of the bar itself, how far from the left end of the barbell is the center of
Three identical coins lie on three corners of a square 10.0 cm on a side, as shown in Figure P7.16. Determine the x and y coordinates of the center of gravity of the three coins. 10 y (cm) FIGURE
Hold your arm out- stretched so that it is horizontal. Estimate the mass of your arm and the position of its center of gravity. What is the gravitational torque on your arm in this position, computed
A solid cylinder sits on top of a solid cube as shown in Figure P7.18. How far above the table's surface is the center of gravity of the combined object? 5.0 cm 400 g 5.0 cm 800 g FIGURE P7.18
Two thin beams are joined end-to-end as shown in Figure P7.23 to make a single object. The left beam is 10.0 kg and 1.00 m long and the right one is 40.0 kg and 2.00 m long. a. How far from the left
Figure P7.24 shows two thin beams joined at right angles. The vertical beam is 15.0 kg and 1.00 m long and the horizontal beam is 25.0 kg and 2.00 m long.a. Find the center of gravity of the two
A regulation table tennis ball has a mass of 2.7 g and is 40 mm in diameter. What is its moment of inertia about an axis that passes through its center?
A solid cylinder with a radius of 4.0 cm has the same mass as a solid sphere of radius R. If the cylinder and sphere have the same moment of inertia about their centers, what is the sphere's radius?
The left part of Figure P7.30 shows a bird's-eye view of two identical balls connected by a light rod that rotates about a vertical axis through its center. The right part shows a ball of twice the
A bicycle rim has a diameter of 0.65 m and a moment of inertia, measured about its center, of 0.19 kg. m2. What is the mass of the rim?
A small grinding wheel has a moment of inertia of 4.0 x 10-5 kg • m2. What net torque must be applied to the wheel for its angular acceleration to be 150 rad/s2?
While sitting in a swivel chair, you push against the floor with your heel to make the chair spin. The 7.0 N frictional force is applied at a point 40 cm from the chair's rotation axis, in the
The 2.5 kg object shown in Figure P7.36 has a moment of inertia about the rotation axis of 0.085 kg • m3. The rotation axis is horizontal. When released, what will be the object's initial angular
A 200 g, 20-cm-diameter plastic disk is spun on an axle through its center by an electric motor. What torque must the motor supply to take the disk from 0 to 1800 rpm in 4.0 s?
A frictionless pulley, which can be modeled as a 0.80 kg solid cylinder with a 0.30 m radius, has a rope going over it, as shown in Figure P7.37. The tension in the rope is 10 N on one side and 12 N
If you lift the front wheel of a poorly maintained bicycle off the ground and then start it spinning at 0.72 rev/s, friction in the bearings causes the wheel to stop in just 12 s. If the moment of
A toy top with a spool of diameter 5.0 cm has a moment of inertia of 3.0×10-5 kg • m2 about its rotation axis. To get the top spinning, its string is pulled with a tension of 0.30 N. How long does
A 34-cm-diameter potter's wheel with a mass of 20 kg is spinning at 180 rpm. Using her hands, a potter forms a pot, centered on the wheel, with a 14 cm diameter. Her hands apply a net friction force
A 1.5 kg block and a 2.5 kg block are attached to opposite ends of a light rope. The rope hangs over a solid, frictionless pulley that is 30 cm in diameter and has a mass of 0.75 kg. When the blocks
A bicycle with 0.80-m-diameter tires is coasting on a level road at 5.6 m/s. A small blue dot has been painted on the tread of the rear tire.a. What is the angular speed of the tires? b. What is the
A 1.2 g pebble is stuck in a tread of a 0.76-m-diameter auto- mobile tire, held in place by static friction that can be at most 3.6 N. The car starts from rest and gradually accelerates on a straight
The graph in Figure P7.45 shows the angular velocity of the crankshaft in a car. Draw a graph of the angular acceleration versus time. Include appropriate numerical scales on both axes. w
Three 0.10 kg balls are connected by light rods to form an equilateral triangle with a side length of 0.30 m. What is the moment of inertia of this triangle about an axis perpendicular to its plane
A reasonable estimate of the moment of inertia of an ice skater spinning with her arms at her sides can be made by modeling most of her body as a uniform cylinder. Suppose the skater has a mass of 64
A 1.5 kg block is connected by a rope ac ross a 50-cmdi ameter, 2.0 kg, frictionless puUey, as shown in Figure P7.62. A constant 10 N tension is applied to the other end of the rope. Starting from
A tradesman sharpens a knife by pushing it against the rim of a grindstone. The 30-cm-diameter stone is spinning at 200 rpm and has a mass of 28 kg. The coefficient of kinetic friction between the
To perform this maneuver, the dancer relies on the fact that the position of her center of gravity.A. Is near the center of the torso. B. Is determined by the positions of her arms and legs. C.
Suppose you wish to make a vertical leap with the goal of getting your head as high as possible above the ground. At the top of your leap, your arms should be A. Held at your sides. B. Raised above
When the dancer is in the air, is there a gravitational torque on her? Take the dancer's rotation axis to be through her center of gravity.A. Yes, there is a gravitational torque. B. No, there is
In addition to changing her center of gravity, a dancer may change her moment of inertia. Consider her moment of inertia about a vertical axis through the center of her body. When she raises her arms
An object is acted upon by two (and only two) forces that are of equal magnitude and oppositely directed. Is the object necessarily in static equilibrium?
A 64 kg woman stands on a very light, rigid board that rests on a bathroom scale at each end, as shown in Figure P8.1. What is the reading on each of the scales? FIGURE P8.1 1.5 m 2.0 m
Suppose the woman in Figure P8.1 is 54 kg, and the board she is standing on has a 10 kg mass. What is the reading on each of the scales? FIGURE P8.1 1.5 m 2.0 m
How close to the right edge of the 56 kg picnic table shown in Figure P8.3 can a 70 kg man stand without the table tipping over?Figure P8.3 0.74 m 2.10 m 0.55 m

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