Questions and Answers of Physics Everyday Phenomena

A boy pushes his friend across a skating rink. Since the frictional forces are very small, the force exerted by the boy on his friend’s back is the only significant force acting on the friend in
A crate on rollers is pushed up an inclined plane into a truck. The pushing force required is less than half the force that would be needed to lift the crate straight up into the truck. Does the
A lever is used to lift a rock as shown in the diagram. Will the work done by the person on the lever be greater than, equal to, or less than the work done by the lever on the rock? Explain. Q3
A woman uses a pulley arrangement to lift a heavy crate. She applies a force that is one-fourth the weight of the crate, but moves the rope a distance four times the height that the crate is lifted.
A man walks across the room. What forces act on the man during this process? Which, if any, of these forces do work on the man? Explain.
A ball is being twirled in a circle at the end of a string. The string provides the centripetal force needed to keep the ball moving in the circle at constant speed. Does the force exerted by the
In the situation pictured in question 3, does the normal force of the floor pushing upward on the block do any work? Explain.
In the situation pictured in question 3, if there is a frictional force opposing the motion of the block, does this frictional force do work on the block? Explain.
A string is used to pull a wooden block across the floor without accelerating the block. The string makes an angle to the horizontal as shown in the diagram. a. Does the force applied via the
Equal forces are used to move blocks A and B across the floor. Block A has twice the mass of block B, but block B moves twice the distance moved by block A. Which block, if either, has the greater
The period of the moon’s orbit about the Earth is 27.3 days, but the average time between full moons is approximately 29.3 days. The difference is due to the motion of the Earth about the sun.a.
The sun’s mass is 1.99 x 1030 kg, the Earth’s mass is 5.98 x 1024 kg, and the moon’s mass is 7.36 x 1022 kg. The average distance between the moon and the Earth is 3.82 x 108 m, and the average
Assume that a passenger in a rollover accident must turn through a radius of 3.0 m to remain in the seat of the vehicle. Assume also that the vehicle makes a complete turn in 1 second.a. Using the
A car with a mass of 900 kg is traveling around a curve with a radius of 60 m at a constant speed of 25 m/s (56 MPH). The curve is banked at an angle of 15 degrees.a. What is the magnitude of the
A Ferris wheel with a radius of 12 m makes one complete rotation every 8 seconds.a. Using the fact that the distance traveled by a rider in one rotation is 2πr, the circumference of the wheel, find
A 0.20-kg ball is twirled at the end of a string in a horizontal circle with a radius of 0.60 m. The ball travels with a constant speed of 4.0 m/s.a. What is the centripetal acceleration of the
The acceleration of gravity at the surface of the moon is approximately 1⁄ 6 that at the surface of the Earth (9.8 m/s2). What is the weight of an astronaut standing on the moon whose weight on
Two masses are attracted by a gravitational force of 0.14 N. What will the force of attraction be if the distance between these two masses is halved?
Two 200-kg masses (440 lb) are separated by a distance of 1 m. Using Newton’s law of gravitation, find the magnitude of the gravitational force exerted by one mass on the other.
Two masses are attracted by a gravitational force of 0.36 N. What will the force of attraction be if the distance between the two masses is tripled?
Joe has a weight of 720 N (about 162 lb) when he is standing on the surface of the Earth. What would his weight (the gravitational force due to the Earth) be if he doubled his distance from the
What is the ratio of the Earth’s orbital period about the sun to the Earth’s period of rotation about its own axis?
The time separating high tides is 12 hours and 25 minutes. If high tide occurs at 2:10 P.M. one afternoon:a. At what time will high tide occur the next afternoon?b. When would you expect low tides to
The acceleration of gravity on the surface of Jupiter is 26.7 m/s2. What is the weight on Jupiter of a woman whose weight on Earth is 110 lb?
A Ferris wheel at a carnival has a radius of 12 m and turns so that the speed of the riders is 8 m/s.a. What is the magnitude of the centripetal acceleration of the riders?b. What is the magnitude of
A car with a mass of 1000 kg travels around a banked curve with a constant speed of 27 m/s (about 60 MPH). The radius of curvature of the curve is 40 m.a. What is the centripetal acceleration of the
A car with a mass of 1200 kg is moving around a curve with a radius of 40 m at a constant speed of 20 m/s (about 45 MPH).a. What is the centripetal acceleration of the car?b. What is the magnitude of
A 0.25-kg ball moving in a circle at the end of a string has a centripetal acceleration of 4 m/s2. What is the magnitude of the centripetal force exerted by the string on the ball to produce this
How much larger is the required centripetal acceleration for a car rounding a curve at 60 MPH than for one rounding the same curve at 30 MPH?
A ball traveling in a circle with a constant speed of 3 m/s has a centripetal acceleration of 9 m/s2. What is the radius of the circle?
A car rounds a curve with a radius of 25 m at a speed of 20 m/s. What is the centripetal acceleration of the car?
A ball is traveling at a constant speed of 5 m/s in a circle with a radius of 0.8 m. What is the centripetal acceleration of the ball?
Would tides exist if the gravitational force did not depend upon the distance between objects? Explain.
Why is there a high tide rather than a low tide when the moon is on the opposite side of the Earth from the ocean and the gravitational pull of the moon on the water is the weakest? Explain.
Since the Earth rotates on its axis once every 24 hours, why don’t high tides occur exactly twice every 24 hours? Explain.
Is Kepler’s third law valid for artificial satellites orbiting about the Earth? Explain.
A synchronous satellite is one that does not move relative to the surface of the Earth; it is always above the same location. Why does such a satellite not just fall straight down to the Earth?
During what phase of the moon can a solar eclipse occur? Explain.
Are we normally able to see the new moon? Explain.
At what times of the day or night does the half-moon rise or set? Explain.
At what times during the day or night would you expect the new moon to rise and set? Explain.
A painter depicts a portion of the night sky as shown in the diagram below, showing the stars and a crescent moon. Is this view possible? Explain. Q24 Diagram
Two masses are separated by a distance r. If this distance is doubled, is the force of interaction between the two masses doubled, halved, or changed by some other amount? Explain.
Three equal masses are located as shown in the diagram. What is the direction of the net force acting upon m2? Explain. mз m2 m, Q22 Diagram
Is there a net force acting on the planet Earth? Explain.
Does the sun exert a larger force on the Earth than that exerted on the sun by the Earth? Explain.
Does a planet moving in an elliptical orbit about the sun move fastest when it is farthest from the sun or when it is nearest to the sun? Explain by referring to one of Kepler’s laws.
Consider the method of drawing an ellipse pictured in figure 5.15. How would we modify this process to make the ellipse into a circle, which is a special case of an ellipse? Explain. Focus
How did Kepler’s view of the solar system differ from that of Copernicus? Explain.
Heliocentric models of the solar system (Copernican or Keplerian) require that the Earth rotate on its axis producing surface speeds of roughly 1000 MPH. If this is the case, why do we not feel this
Did Ptolemy’s view of the solar system require motion of the Earth, rotational or otherwise? Explain.
In what way did the heliocentric view of the solar system proposed by Copernicus provide a simpler explanation of planetary motion than the geocentric view of Ptolemy? Explain.
Sketch the forces acting upon a rider on a Ferris wheel when the rider is at the top of the cycle, labeling each force clearly. Which force is largest at this point, and what is the direction of the
If a ball is whirled in a vertical circle with constant speed, at what point in the circle, if any, is the tension in the string the greatest? Explain.
If a curve is banked, is it possible for a car to negotiate the curve even when the frictional force is zero due to very slick ice? Explain.
Is there a maximum speed at which the car in question 9 will be able to negotiate the curve? If so, what factors determine this maximum speed? Explain.
A car travels around a flat (nonbanked) curve with constant speed.a. Sketch a diagram showing all of the forces acting on the car.b. What is the direction of the net force acting on the car? Explain
For a ball being twirled in a horizontal circle at the end of a string, does the vertical component of the force exerted by the string produce the centripetal acceleration of the ball? Explain.
Before the string breaks in question 6, is there a net force acting upon the ball? If so, what is its direction? Explain.
The centripetal acceleration depends upon the square of the speed rather than just being proportional to the speed. Why does the speed enter twice? Explain.
A ball on the end of a string is whirled with constant speed in a counterclockwise horizontal circle. At point A in the circle, the string breaks. Which of the curves sketched below most accurately
A car travels the same distance at constant speed around two curves, one with twice the radius of curvature of the other. For which of these curves is the change in velocity of the car greater?
Two cars travel around the same curve, one at twice the speed of the other. After traveling the same distance, which car, if either, has experienced a larger change in velocity? Explain.
A car travels around a curve with constant speed.a. Does the velocity of the car change in this process? Explain.b. Is the car accelerated? Explain.
Suppose that the speed of a ball moving in a horizontal circle is increasing at a steady rate. Is this increase in speed produced by the centripetal acceleration? Explain.
A sky diver has a weight of 750 N. Suppose that the air resistive force acting on the diver increases in direct proportion to his velocity such that for every 10 m/s that the diver’s velocity
A 60-kg man is in an elevator that is accelerating downward at the rate of 1.4 m/s2.a. What is the true weight of the man in newtons?b. What is the net force acting on the man required to produce the
Two blocks tied together by a horizontal string are being pulled across the table by a horizontal force of 30 N as shown. The 2-kg block has a 6-N frictional force exerted on it by the table, and the
A 60-kg crate is lowered from a loading dock to the floor using a rope passing over a fixed support. The rope exerts a constant upward force on the crate of 500 N.a. Will the crate accelerate?
A dish with a mass 0.4 kg has a force of kinetic friction of 0.15 N exerted on it by a moving tablecloth for a time of 0.2 s.a. What is the acceleration of the dish?b. What velocity does it reach in
A rope exerts a constant horizontal force of 250 N to pull a 60-kg crate across the floor. The velocity of the crate is observed to increase from 1 m/s to 3 m/s in a time of 2 seconds under the
A constant horizontal force of 30 N is exerted by a string attached to a 5-kg block being pulled across a tabletop. The block also experiences a frictional force of 5 N due to contact with the
A 60-kg woman in an elevator is accelerating upward at a rate of 1.2 m/s2.a. What is the net force acting upon the woman?b. What is the gravitational force acting upon the woman?c. What is the normal
An upward force of 18 N is applied via a string to lift a ball with a mass of 1.5 kg. a. What is the net force acting upon the ball? b. What is the acceleration of the ball?
A 0.5-kg book rests on a table. A downward force of 6 N is exerted on the top of the book by a hand pushing down on the book.a. What is the magnitude of the gravitational force acting upon the
At a given instant in time, a 5-kg rock is observed to be falling with an acceleration of 7.0 m/s2. What is the magnitude of the force of air resistance acting upon the rock at this instant?
At a given instant in time, a 4-kg rock that has been dropped from a high cliff experiences a force of air resistance of 15 N. What are the magnitude and direction of the acceleration of the rock?
Who has the larger mass, a man weighing 145 lb or one weighing 735 N?
The author of this text has a weight of 600 N.a. What is his mass in kilograms?b. What is his weight in pounds? (1 lb = 4.45 N)
Jennifer has a weight of 110 lb.a. What is her weight in newtons? (1 lb = 4.45 N)b. What is her mass in kilograms?
What is the mass of a 196-N weight?
What is the weight of a 40-kg mass?
A 4-kg sled sliding freely on an icy surface experiences a 2-N frictional force exerted by the ice and an air-resistive force of 0.5 N.a. What is the net force acting on the sled?b. What is the
A 4-kg block is acted upon by three horizontal forces as shown in the diagram.a. What is the net horizontal force acting on the block?b. What is the horizontal acceleration of the block? 10 N 5
Two forces, one of 50 N and the other of 30 N, act in opposite directions on a box as shown in the diagram. What is the mass of the box if its acceleration is 4.0 m/s2? 50 N 30 N E7 Diagram
A 6-kg block being pushed across a table by a force P has an acceleration of 3.0 m/s2.a. What is the net force acting upon the block?b. If the magnitude of P is 20 N, what is the magnitude of the
A pulled tablecloth exerts a frictional force of 0.6 N on a plate with a mass of 0.4 kg. What is the acceleration of the plate?
A 3.0-kg block being pulled across a table by a horizontal force of 80 N also experiences a frictional force of 5 N. What is the acceleration of the block?
A net force of 20 N acting on a wooden block produces an acceleration of 4.0 m/s2 for the block. What is the mass of the block?
A ball with a mass of 2.5 kg is observed to accelerate at a rate of 6.0 m/s2. What is the size of the net force acting on this ball?
A single force of 40 N acts upon a 5-kg block. What is the magnitude of the acceleration of the block?
If the elevator cable breaks and you find yourself in a condition of apparent weightlessness as the elevator falls, is the gravitational force acting upon you equal to zero? Explain.
If you get into an elevator on the top floor of a large building and the elevator begins to accelerate downward, will the normal force pushing up on your feet be greater than, equal to, or less than
Suppose that a sky diver wears a specially lubricated suit that reduces air resistance to a small constant force that does not increase as the diver’s velocity increases. Will the sky diver ever
Two blocks with the same mass are connected by a string and are pulled across a frictionless surface by a constant force, F, exerted by a string (see diagram).a. Will the two blocks move with
Two masses, m1 and m2, connected by a string, are placed upon fixed friction less pulley as shown in the diagram. If m2 is larger than m1, will the two masses accelerate? Explain. m2 m1 Q29 Diagram
A toy battery-powered tractor pushes a book across a table. Draw separate diagrams of the book and the tractor identifying all of the forces that act upon each object. What is the reaction force
The upward normal force exerted by the floor on a chair is equal in size but opposite in direction to the weight of the chair. Is this equality an illustration of Newton’s third law of motion?
A mule is attempting to move a cart loaded with rock. Since the cart pulls back on the mule with a force equal in size to the force that the mule exerts on the cart (according to Newton’s third
A sprinter accelerates at the beginning of a 100-meter race and then tries to maintain maximum speed throughout the rest of the race.a. What external force is responsible for accelerating the runner

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