Q&A Hero

Q: Your lab instructor projects a ball horizontally from a lab bench that lands on the floor a horizontal distance away. Compared with the time the ball would take if simply dropped vertically from the bench, the time in the air for the projected ball is 1) less. 2) the same. 3) greater. The horizontal distance from the bottom of the bench the ball travels in hitting the floor is equal the ball's initial speed 4) multiplied by its time in the air. 5) coupled with its speed of fall. 6) squared plus its downward speed squared when hitting the floor.

Q: A garden hose is held at an angle of 50o. Neglecting air resistance, the water will travel exactly the same horizontal distance before returning to the same level if the hose is held at an angle of 1) 40o. 2) 45o. 3) 60o. For maximum range, the hose should be held at 4) 40o. 5) 45o. 6) 55o. 7) 60o.

Q: A projectile is launched vertically upward at 40 m/s. If air resistance is negligible, its speed upon returning to its starting point is 1) less than 40 m/s. 2) 40 m/s. 3) more than 40 m/s. All along the ball's trajectory, its acceleration is 4) g downward. 5) g at an angle. 6) zero. If air resistance does affect motion, then the ball's speed upon returning to its starting point is 7) less than 50 m/s. 8) 50 m/s. 9) more than 50 m/s.

Q: In the absence of air resistance, a projectile launched at the same speed at any angle will attain the greatest range when projected at 1) 30o. 2) 45o. 3) 60o. 4) 90o. In the case of throwing a heavy spear, not at the same speed but with the same force, the greatest range is attained more likely when thrown at 5) 30o. 6) 45o. 7) 60o. 8) 90o.

Q: Figure N-8 The trajectory of a cannonball fired from a canon depends on 1) the initial velocity. 2) the angle of projection. 3) the effects of air resistance. 4) all of these. When air resistance does affect motion, the cannonball doesn't travel 5) as high. 6) as far. 7) as high and as far.

Q: Figure N-7 Ball A is dropped from rest as ball B is shot out horizontally. Ball A hits the ground 1) before ball B. 2) after ball B. 3) at the same time as ball B. This is because 4) ball A has less distance to travel. 5) ball B is acted upon by an additional force. 6) both balls fall the same vertical distance with the same acceleration.

Q: The Moon does not fall to Earth because 1) the net force on it is zero. 2) it is being pulled by the sun and planets as well as Earth. 3) it is beyond the main pull of Earth's gravity. 4) but it does fall! More specifically, the Moon 5) is subject to both centripetal and centrifugal forces. 6) interacts with all massive bodies, both near and far. 7) is free of air resistance as well as other Earthly influences. 8) continually falls around Earth rather than straight into it.

Q: Earth is closer to the Sun in winter than in summer. The orbital speed of Earth about the Sun is therefore faster during the 1) summer. 2) winter. 3) is the same for all seasons. Correspondingly, the gravitational force between the Sun and Earth is strongest during 4) summer. 5) winter. 6) is the same for all seasons.

Q: The body chiefly responsible for ocean tides is the 1) Moon, 2) Sun, chiefly because 3) the Moon is closer to Earth than the sun. 4) gravitational pull by the Moon is less than that of the sun. 5) the difference between the Moon's pull on the near and far sides of Earth is appreciable.

Q: Figure G-2 Suppose masses M1 and M2 are falling toward planet M under gravitational influence. We would find that M1 falls 1) faster than M2, 2) as fast as M2, 3) slower than M2, with the result that 4) ocean tides are formed on M. 5) the distance between M1 and M2 increases. 6) the distance between M1 and M2 decreases. 7) the distance between M1 and M2 remains unchanged, but the distance between M and M1 decreases.

Q: A lunar month is about 28 days. If the Moon were closer to Earth than it now is, the lunar month would be 1) less than 28 days, 2) more than 28 days, 3) still 28 days, mainly because 4) centripetal force would lessen with decreased distance. 5) a closer Moon means an increase in both gravitational force and speed, which in a smaller orbit means shorter time. 6) orbital speed about the center of mass of Earth-Moon system is not dependent upon the distance between Earth and Moon. 7) of tidal friction.

Q: If the Moon were covered with water, it would have 1) one high tidal bulge, 2) two high tidal bulges, 3) three high tidal bulges, 4) no tidal bulges, which would follow from 5) the same reason that Earth has two high tidal bulges. 6) no centrifugal force tide would exist on the Moon. 7) the Moon being much less massive than Earth. 8) the center of mass of Earth-Moon system that lies halfway to the Moon.

Q: High tides are predominately produced by the 1) strong gravitational pull of the Sun, 2) centrifugal force created by Earth-Moon orbit, 3) differences in gravitational pulls of the Moon on opposite sides of Earth, which is due to 4) rotation of Earth and Moon about the Sun. 5) Moon pulling with significantly more force on the closer side of Earth than on the farther side. 6) the Sun's pull on Earth being 200 times stronger than Moon's gravitational pull.

Q: Figure G-1 Pretend an object is set sliding on a huge frictionless plane in contact with the surface of Earth as shown. Once the object is set in motion it will 1) theoretically slide to the right forever 2) slide back and forth 3) slow down and stop because 4) of its inertia. 5) gravitational force decreases with increasing distance. 6) the object is sliding "uphill" and then "downhill" relative to the round Earth.

Q: If the mass of Earth somehow increased with no change in radius, your weight would 1) increase also. 2) decrease. 3) remain the same. If instead, both Earth's mass and its radius doubled, your weight at Earth's surface would be 4) half before the changes. 5) the same as before the changes. 6) twice. 7) four times greater.

Q: Earth and the Moon are attracted to each other by gravitational force. The more-massive Earth attracts the less-massive Moon with a force 1) less than the force that Moon exerts on Earth. 2) greater than that of the force that Moon exerts on Earth. 3) the same as that of the force that Moon exerts on Earth. This is in accord with 4) the law of inertia. 5) Kepler's Laws. 6) the conservation of energy. 7) the fact that both Moon and Earth orbit about a common point, the center of mass. 8) the law of action and reaction.

Q: A 400-N person stands on the surface of Earth. If he were somehow able to stand on a ladder so that he was twice as far from the center of Earth, he would weigh 1) 0 N. 2) 100 N. 3) 200 N. 4) 400 N. This would be because 5) he would be above the atmosphere. 6) his mass would be the same wherever he was. 7) the force due to gravity obeys the inverse square law.

Q: A woman standing on the surface of Earth has a mass of 70 kg and a weight of 700 N. If instead she is floating freely inside a non-rotating space habitat far from Earth, her mass would be 1) less than 70 kg 2) 70 kg 3) more than 70 kg and her weight would be 4) less than 700 N. 5) 700 N. 6) more than 700 N.

Q: As a spaceship nears the Moon, its mass 1) varies slightly with distance, 2) increases, 3) decreases, 4) remains unchanged, while the Moon's gravitation force on the ship 5) increases. 6) decreases. 7) remains unchanged.

Q: A very massive body A and a less massive body B move toward each other under the influence of gravity. Compared to the force on A, the force on B is 1) greater. 2) the same. 3) less. As A and B get closer and closer, each experiences an increase in 4) velocity. 5) acceleration. 6) force. 7) all of these. 8) none of these.

Q: Figure T-3 The 50-kg stuntman places a 50-kg uniform 6-meter plank on top of a skyscraper and stands on the tip of it that overhangs the building as shown. What is the approximate distance that the overhang can be extended without disaster? 1) 0.5 m 2) 1 m 3) 1.5 m If the 6-meter board has a mass of only 25 kilograms, then the maximum overhang distance would be about 5) 0.5 m. 6) 1 m. 7) 1.5 m. 8) 2 m.

Q: Figure T-2 The heavy boy and light girl are balanced on the seesaw. If they both move inward so that each is exactly half the original distance from the pivot, then the 1) boy's end will move downward. 2) girl's end will move downward. 3) seesaw will remain in balance. If the fulcrum of the seesaw is repositioned so each can sit at an END of the board and be in balance, then if each moves inward half way the 4) boy's end will move downward. 5) girl's end will move downward. 6) seesaw will remain balanced.

Q: Figure E-4 The center of gravity for each truck is marked X. Which truck(s) will tip over? 1) Truck 1 2) Truck 2 3) Truck 3 4) All will tip. This is because 5) its center of gravity is highest. 6) its center of gravity is lowest. 7) its center of gravity lies beyond a point of support. 8) all the centers of gravity lie above the wheelbases.

Q: Figure T-1 The boy plays "solitary seesaw" as shown. We can understand this by imagining that he has an invisible partner who is actually at the 1) fulcrum. 2) right end of the board. 3) rotational inertia of the seesaw as a whole. 4) seesaw's center of gravity. Since the seesaw is not rotating, we can say that 5) the net torque on the seesaw is zero. 6) potential energy and kinetic energy are equal to each other. 7) the boy's and the seesaw's centers of gravity must be equal distances from the fulcrum. 8) the boy and the seesaw must have the same weight.

Q: Jocko the clown at the top of a tall flagpole has considerable potential energy relative to the circus net below. After stepping off the pole and neglecting air resistance, his potential energy when he is half way to the net is 1) the same as at the top, 2) one quarter the amount at the top, 3) one half the amount at the top, 4) more than one-half the amount at the top, and compared to his kinetic energy when meeting the net, his kinetic energy at the half-way point is 5) one half. 6) the same as his potential energy at the half-way point. 7) both of these 8) neither of these

Q: Figure E-6 In the hydraulic device shown, when the small piston is pushed down 10 cm with a force of 10 N, the large piston is raised 1 cm. This means that the large piston is capable of lifting 1) 10 N, 2) 100 N, 3) 1000 N, 4) any amount of weight, which illustrates 5) that impulse is equal to a change in momentum. 6) (F d) input = (F d) output. 7) Newton's second law. 8) that the stored energy that a body possesses may be transformed into other forms of energy.

Q: E.

Q: Figure E-5 A small bead slides without friction along the wire shown. It begins at A and slides by gravity past B, which doesn't touch the rest of the wire. The potential energy of the bead is greatest at point 1) A, 2) B, 3) C, 4) D, 5) E, and the bead has its maximum momentum at point 6) A. 7) B. 8) C. 9) D.

Q: All things being practically equal, if the energy content in gasoline were doubled, then the distance a car should travel per liter of gasoline should 1) be no different. 2) double. 3) quadruple. If the low-energy and high-energy fuels are burned in the same time, then compared to the POWER produced by combustion of the low-energy gasoline, the power produced by the combustion of the higher-energy gasoline should 4) be no different. 5) double. 6) quadruple.

Q: Figure E-3 To lift the 5000-N block, the man finds that he must pull 10 m of rope through his hands for every 1 m the block rises. Neglecting the weights of the pulleys and friction, how hard must the man pull on the rope to raise the block? 1) 5 N 2) 50 N 3) 500 N 4) 5000 N which is in accord with 5) Newton's second law. 6) that impulse equals change in momentum. 7) (F d) input = (F d) output. 8) mechanical energy can be stored as potential energy.

Q: Figure E-2 A pendulum bob swings to and fro as shown in the sketch. The kinetic energy of the bob 1) is maximum at position A, 2) is maximum at position B, 3) is the same at all positions, and the potential energy is maximum at position 4) A. 5) B. 6) is the same at all positions.

Q: Figure E-1 A marble rolls back and forth along the path shown. When it is at position B, its kinetic energy is 1) maximum, 2) minimum, 3) midway between maximum and minimum, its momentum is 4) maximum, 5) minimum, 6) midway between maximum and minimum, and its potential energy is 7) maximum. 8) minimum. 9) midway between maximum and minimum.

Q: A golf ball moving forward with 1 unit of momentum strikes a heavy bowling ball that is initially at rest. After the golf ball bounces backward, the bowling ball is in motion with a momentum that must be 1) 1 unit. 2) more than 1 unit. 3) less than 1 unit. The magnitude of the golf ball's momentum after collision must be somewhat less than 1 unit, for otherwise a violation would occur in the conservation of 4) energy. 5) momentum. 6) both. 7) neither.

Q: If in the absence of external forces, a rotating ball of hot gas cools and contracts, its rate of rotation 1) decreases 2) remains essentially the same 3) increases and its angular momentum 4) decreases. 5) remains essentially the same. 6) increases.

Q: If the polar ice caps melted and flowed toward the equator, the rotation of Earth would tend to 1) decrease in angular speed, 2) be unchanged, 3) increase in angular speed, with the result that the day would be 4) slightly longer. 5) slightly shorter. 6) unaffected.

Q: An open freight car rolls friction free along a horizontal track in a pouring rain that falls vertically. As water accumulates in the car, the car's speed 1) increases. 2) decreases. 3) remains the same. This is best explained by the principle of 4) inertia. 5) momentum conservation. 6) energy conservation. 7) Newton's 2nd law.

Q: When the momentum of a punch is stopped by the fighter's jaw while he moves into the oncoming punch, the result is 1) an increase in the relative velocity of the blow, 2) a decrease in the time of contact of the blow, which thereby most greatly increases the 3) force. 4) impulse. 5) momentum. 6) inertia. 7) energy.

Q: When the momentum of a punch is stopped by the fighter's jaw, he "rides with the punch" so as to 1) decrease the velocity of the blow, 2) increase the time of contact of the blow, and thereby reduce the 3) force. 4) impulse. 5) momentum. 6) energy.

Q: We can apply the equationFt = change in (mv) to the case of a baseball player striking a pitched ball. To impart the maximum change in momentum, mv, to the ball, the batter hits the ball with the greatest force he can muster and he also 1) extends the time of contact as much as possible by "following through." 2) makes the time of contact as short as possible, thereby increasing the force. 3) none of the above! In the impulse-momentum equation applied to hitting the ball, the "v" represents 4) the velocity of the bat. 5) the velocity of the ball. 6) a vector quantity.

Q: A sports car and a moving van move at the same speed when they crash into a cement wall and stop equally quickly. The vehicle to have the greater force of impact will be 1) the sports car, 2) the van, 3) neither, for they experience equal forces of impact because 4) they are traveling at the same speed. 5) the van's momentum is much greater. 6) the sport car has a greater change in velocity upon impact. 7) they both have equal momentum.

Q: A freight car rolls along a horizontal track at 12 m/s and hooks onto an identical freight car at rest. The coupled cars will 1) come to a quick stop, 2) roll at 3 m/s, 3) roll at 6 mph, 4) roll at 12 ms, which makes sense because 5) in the absence of external forces, trains in motion continue in motion. 6) the acceleration of the car at rest equals the force of impact divided by the two masses. 7) since twice the mass is moving, the speed will be half for the same momentum. 8) energies before and after the collision remain the same.

Q: According to the equation Ft = change in (mv), a foam rubber dashboard is safer than a metal one, for the force of impact, F, of an occupant against the dash is lessened in an accident. In this case, the "m" in this equation represents the 1) mass of the car, 2) mass of the person, 3) momentum of the car, 4) momentum of the person, and the "v" represents the 5) velocity of the car. 6) speed at which the person hits the dashboard. 7) relative velocity between cars in a collision. 8) change in velocity, which is 10 m/s2.

Q: A ball is thrown against a wall, bounces off, and is caught. The number of impulses acting on the ball is 1) one. 2) two. 3) three. 4) none. The greatest impulse occurs when the ball 5) is thrown. 6) bounces against the wall. 7) is caught. 8) is zero for each. 9) is nonzero, but the same for each case.

Q: Figure N-11 As the ball rolls from the straight path from A to B its velocity increases and its acceleration 1) increases, 2) decreases, 3) remains constant, and as it rolls from B to C its acceleration along the path 4) increases. 5) decreases. 6) remains constant.

Q: Figure N-10 As the ball rolls from A to B its velocity increases and its acceleration 1) increases; 2) decreases; 3) remains constant; and when it rolls from B to C its acceleration along the path 4) increases. 5) decreases. 6) remains constant.

Q: A skydiver jumps through the air from a high-flying plane. As her velocity of fall increases, the net force acting on her 1) increases also, 2) decreases, 3) remains unchanged, and her acceleration 4) increases. 5) decreases. 6) remains unchanged.

Q: A stone is thrown downward from a tall cliff and hits the ground below. If it were instead thrown straight upward with the same initial speed, it would end up striking the ground below (neglect air resistance) with 1) the same speed. 2) less speed. 3) greater speed. If air resistance IS a factor, then when the stone is moving downward it will undergo 4) an increase in acceleration as velocity increases. 5) a decrease in acceleration as velocity increases. 6) a constant acceleration.

Q: A horizontal 100-N force exerted against a 1000-N block causes the block to slide on a level surface with constant velocity. The friction force on the block must be 1) zero. 2) 100 N. 3) 1000 N. 4) greater than 1000 N. In this case the pushing force and the friction force are 5) equal but oppositely directed. 6) an action-reaction pair. 7) both of these. 8) none of these.

Q: If a constant net force is applied to a body, the body is 1) accelerating. 2) moving at constant speed. 3) at rest or moving at constant velocity. If a body is moving at constant velocity, it must have 4) a constant net force acting upon it. 5) constant non-zero acceleration. 6) constant speed. 7) none of the above.

Q: A 200-N weight hangs motionless from a string that is attached to the ceiling. The net force acting on the weight is 1) zero, 2) 100 N, 3) 200 N, and if the string breaks, the net force acting on the weight will be 4) zero. 5) 100 N. 6) 200 N.

Q: The net force that acts on a 100-N freely falling body is 1) zero, 2) 9.8 N, 3) 100 N, and its acceleration is 4) zero. 5) 9.8 m/s2. 6) 100 m/s2.

Q: If you push with 200 N of force against your 1500-N refrigerator and it slides across your kitchen floor at constant velocity, friction of the floor against the refrigerator must be 1) zero, 2) 200 N, 3) 1300 N, 4) 1500 N, 5) greater than 1500 N, and the force with which you push must be 6) equal and oppositely directed to the friction force. 7) the action force, and the friction the reaction force. 8) both of these. 9) none of these.

Q: Figure N-9 While a ship moves toward the right at constant velocity, a seaman atop the mast drops a stone which freely falls to position 1) A. 2) B. 3) C. This is better understood by realizing that 4) the ship moved to the right a distance equal to that between A and B while the stone fell vertically. 5) the stone was moving to the right just as fast as the ship during the fall. 6) the net force acting on the stone is equal to its weight. 7) because of inertia, the stone experiences a horizontal motion unlike that of the ship. 8) the stone underwent an acceleration while the ship did not.

Q: Figure N-6 Two 50-N weights pull on the scale as shown. The reading on the scale is 1) 0 N. 2) 25 N. 3) 50 N. 4) 100 N. This is clearer to understand if we think of the situation this way: 5) Since no acceleration is taking place, the forces cancel one another. 6) One of the weights "holds" the scale while the other weight stretches the spring. 7) The two hanging weights provide forces that constitute an action/reaction pair.

Q: Figure N-5 The two men compete in a tug of war. Both pull equally and the scale reads 800 newtons. Each man must pull with a force of 1) 400 N. 2) 800 N. 3) 0 N. Consider action and reaction forces in this case: If action is the man on the left pulling on the rope, then the reaction force is 4) the rope pulling on the man on the left. 5) the rope pulling on the man on the right. 6) the man on the right pulling on the rope.

Q: Figure N-4 Each group in a tug-of-war pulls with 1000 N on each side of the rope. The net force on the rope is 1) 0 N 2) 500 N 3) 1000 N 4) 2000 N and the tension within the rope is 5) 0 N. 6) 500 N. 7) 1000 N. 8) 2000 N.

Q: Figure N-2 A 100-N little physics tyke hangs on the ends of a rope suspended over a pulley as shown. The tension in the rope is 1) 0 N. 2) 50 N. 3) 100 N. 4) 200 N. It is interesting to note that 5) the tension in the rope at its midpoint (uppermost part) is 100 N. 6) this is a modified tug-o'-war example (simply draped over a pulley). 7) the net force acting on the rope is in this case identical to the child's weight.

Q: Figure N-3 If an 800-N man hangs motionless from four vertical strands of rope, then the tension in each strand of rope is 1) 0 N 2) 200 N 3) 400 N 4) 800 N which results in a net force on the man of 5) 0 N. 6) 200 N. 7) 400 N. 8) 800 N.

Q: You can exert more force on the pedals of a bicycle if you pull up on the handlebars because 1) your center of gravity can be shifted to a position directly above the pedals, 2) the handlebars, in turn, pull down on you and this force is transmitted to the pedals, 3) rotational inertia is lessened, 4) rotational inertia is increased, all of which illustrates 5) that equilibrium is center-of-gravity dependent. 6) the law of action and reaction. 7) inertia may be both linear and rotational.

Q: Which of the following has the greater weight? 1) 1 kilogram of gold 2) 1 kilogram of feathers 3) both weigh the same in the same locality This follows from the fact that 4) gold is more compact than feathers. 5) weight and mass are directly proportional to each other.

Q: If an object has twice as much mass as another, then it also has twice as much 1) acceleration. 2) weight. 3) center of gravity. 4) area. This is because 5) of inertia. 6) mass and weight are directly proportional to each other. 7) the gravitational force acting on all objects in the same locality is the same.

Q: An elephant and a feather fall through the air. The force of air resistance is 1) greater on the feather 2) greater on the elephant 3) the same on each because 4) the feather weighs less. 5) the elephant encounters more air because of his greater size and speed. 6) each is under the influence of gravitational force alone.

Q: In referring to how much matter a body contains, we use the term 1) volume 2) mass 3) weight and the force of gravitational attraction upon a body is 4) weight. 5) volume. 6) mass.

Q: A profound message from all of science is that we are a part of nature A) that stands above other life forms. B) and have the ability to conquer it. C) that is becoming more and more conscious of itself.

Q: The principle of equivalence tells us that A) mass and energy are forms of each other. B) space and time are forms of each other. C) electricity and magnetism are forms of each other. D) observations made in an accelerating reference frame are indistinguishable from those made in a gravitational field. E) all of the above

Q: Einstein's theory of gravitation A) agrees with established results of Newton's theory. B) has been supported by repeated experiments. C) incorporates Newton's theory as a special case. D) is superior to Newton's where spacetime is more curved. E) all of the above

Q: Compared with Newton's theory of gravity, Einstein's theory is A) an exception to the correspondence principle. B) in accord with the correspondence principle. C) neither of these

Q: If a star 100 light-years away explodes, the time for the gravitational waves to reach Earth is 100 years as measured from A) any uniformly moving reference frame. B) any accelerating reference frame. C) any reference frame, accelerated or not. D) the reference frame of the waves. E) Earth.

Q: If a star that is 10 light-years away from Earth explodes, gravitational waves from the explosion will reach Earth in A) less than 10 years. B) more than 10 years. C) 10 years.

Q: Accelerate an electron and you produce an electromagnetic wave. Accelerate a massive body and you produce A) a gravitational wave. B) a cosmic wave. C) both of these D) neither of these

Q: A measuring stick on a rapidly rotating disk will not appear to shrink if it is oriented along the A) circumference. B) radius. C) either of these D) neither of these

Q: Strictly speaking, the sum of the angles on a triangle equals 180 degrees A) in flat space. B) on a spherical surface. C) on a saddle-shaped surface. D) all or any of the above E) none of the above

Q: The geometry of our universe is A) flat. B) positively curved. C) negatively curved. D) all of the above E) none of the above

Q: Strictly speaking, the ratio of circumference to diameter for a circle equals π as we know it A) in flat space. B) on a spherical surface. C) on a saddle-shaped surface. D) all or any of the above E) none of the above

Q: The measured ratio of circumference to diameter on a disk is π when the disk is A) moving at relativistic speeds. B) rapidly rotating. C) at rest. D) all of the above E) none of the above

Q: The shortest distance between two points on a curved surface is a A) straight line. B) geodesic. C) neither of these

Q: The shortest distance between two points in flat Euclidean space is a A) straight line. B) geodesic. C) neither of these

Q: If the elliptical orbit of Mercury were more eccentric, its precession rate would be A) larger. B) smaller. C) the same. D) nonexistent.

Q: If the orbit of Mercury were perfectly circular, its rate of precession would be A) larger. B) smaller. C) the same. D) zero.

Q: Apart from the effects of other planets, the orbit of Mercury precesses because A) Mercury travels faster than any other planet. B) Mercury's orbit is nearly circular. C) of pronounced variations in Mercury's orbit about the Sun.