Q&A Hero

Q: The main reason a person weighs less at the equator than at the poles involves the A) spin of the Earth. B) influence of the Sun, Moon, and all the planets. C) law of action and reaction.

Q: If you balance a broom horizontally on one finger, the center of gravity of the broom will be above your finger, closer to the bristles end than the handle end. If you saw the broom in two pieces at that point and weigh the two parts on a scale, you'll find that the heavier part is the A) bristles part. B) handle part. C) both the same weight

Q: You can safely stand on the overhanging end of a heavy plank that rests on a table. How much overhang depends on your mass and the mass of the plank. If you can stand on the end of a plank that overhangs the edge of the supporting table 1/5 its total length, how massive is the plank compared to your mass? A) 1/3 B) the same C) 2/3 D) 1 and 1/3 times E) more than 1 and 1/3 times

Q: You can safely stand on the overhanging end of a heavy plank that rests on a table. How much overhang depends on your mass and the plank's mass. If you can stand on the end of a plank that overhangs the edge of the supporting table 1/4 its total length, how massive is the plank compared to your mass? A) 1/2 B) the same C) 1 and 1/2 times D) twice E) 4 times

Q: A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 12.5-cm mark. From this information, the mass of the meterstick is A) 1/4 kg. B) 1/2 kg. C) 3/4 kg. D) 1 kg. E) none of the above

Q: A 1-kg rock is suspended from the tip of a horizontal meterstick at the 0-cm mark so that the meterstick barely balances like a seesaw when its fulcrum is at the 25-cm mark. From this information, the mass of the meterstick is A) 1/4 kg. B) 1/2 kg. C) 3/4 kg. D) 1 kg. E) none of the above

Q: When riding at constant velocity on a Segway electric vehicle, your center of mass is A) slightly in front of the point between wheels below. B) slightly behind the point between wheels below. C) directly above the point between wheels below.

Q: Strictly speaking, to weigh less in the Northern Hemisphere, you should move to a location farther A) north (toward the pole). B) south (toward the equator). C) east. D) west.

Q: If Earth rotated more slowly about its axis, your weight would A) increase. B) decrease. C) stay the same. D) be zero.

Q: To kick a football so it won't topple end over end, kick it so the force of impact extends A) above its center of gravity. B) through its center of gravity. C) below its center of gravity.

Q: If Earth had a pair of identical moons on opposite sides of the same circular orbit, the center of gravity of the double-moon-Earth system would be A) inside the Earth, but off center. B) at the center of the Earth. C) outside the Earth, but within the orbital path of the moons. D) outside the Earth, but beyond the orbital path of the moons.

Q: Which of these has its center of mass where no mass exists? A) baseball B) golf ball C) basketball D) none of the above

Q: The famous Leaning Tower of Pisa doesn't topple over because its center of gravity is A) relatively low for such a tall building. B) stabilized by its structure. C) displaced from its center. D) above a place of support. E) in the same place as its center of mass.

Q: The center of mass of a human body is located at a point that A) is fixed, but different for different people. B) is always directly behind the belly button. C) changes as a person bends over. D) none of the above

Q: The long, heavy tail of a spider monkey enables the monkey to easily vary its A) weight. B) momentum. C) inertia. D) center of gravity. E) none of the above

Q: Toss a baseball bat into the air and it wobbles about its A) geometrical center. B) center of mass. C) heavier end.

Q: A boy plays solitary seesaw by placing the seesaw's fulcrum one-eighth the distance from where he sits at one end. Which weighs more? A) the boy B) the seesaw C) they have equal weights D) need more information

Q: A solitary boy cannot balance on a seesaw with its fulcrum at its midpoint. If the fulcrum is moved to one-quarter the distance from the boy, balance is achieved when the weight of the boy is A) less than the weight of the seesaw. B) equal to the weight of the seesaw. C) more than the weight of the seesaw. D) need more information

Q: On a balanced seesaw, a boy three times as heavy as his partner sits A) less than 1/3 the distance from the fulcrum. B) 1/3 the distance from the fulcrum. C) more than 1/3 the distance from the fulcrum.

Q: Two people are balanced on a seesaw. If one person leans inward toward the center of the seesaw, that person's end of the seesaw tends to A) rise. B) fall. C) stay at the same level. D) need more information

Q: To rotate a stubborn screw, it is best to use a screwdriver that has a A) wide handle. B) long handle. C) smooth handle. D) none of the above

Q: A ball gains speed while rolling down a hill due mainly to A) its rotational inertia. B) its angular acceleration. C) a balanced torque. D) an unbalanced torque.

Q: For a system in mechanical equilibrium, the resultant A) force must be zero. B) torque must be zero. C) both of these D) none of these

Q: If you place a pipe over the end of a wrench when trying to rotate a stubborn bolt, effectively making the wrench handle twice as long, you'll multiply the torque by A) two. B) four. C) eight.

Q: A ball that gains speed as it rolls down a hill experiences a A) net torque. B) net force. C) both of these D) neither of these

Q: If Alex wishes to rotate his skateboard, then he must apply a A) torque. B) rotational maneuver. C) pause before bearing down on the board.

Q: A torque acting on an object tends to produce A) equilibrium. B) rotation. C) linear motion. D) velocity. E) a center of gravity.

Q: Compared with a force, a torque involves A) rotation. B) leverage. C) distance from an axis of rotation. D) all the above

Q: Which tin can will roll down an incline in the shortest time, one filled with water or one filled with ice? (Hint: water 'slides' inside the can.) A) with water B) with ice C) both the same D) need more information

Q: Which jar will roll down an incline in the shortest time, an empty one or one filled with peanut butter? A) the empty jar B) both reach the bottom at the same time C) the filled jar D) need more information

Q: Stand a broom upright on the end of its pole and let it topple to the floor. Repeat, but with the bristles end on the floor. The faster fall will be the broom standing on its A) pole-end. B) bristles-end. C) the same either way.

Q: A vertically-held sledge hammer is easier to balance when the heavier end is A) on your hand. B) at the top, away from your hand. C) the same either way

Q: Stand a meterstick on its end and let it rotate to the floor. If you attach a heavy glob of clay to its upper end and repeat, the time to fall will be A) shorter. B) longer. C) the same.

Q: A vertically-held sledge hammer is easier to balance when the heavier end is A) on your hand. B) at the top, away from your hand. C) same either way

Q: A ring, a disk, and a solid sphere begin rolling down a hill together. Which reaches the bottom first? A) ring B) disk C) sphere D) all reach the bottom at the same time E) need more information

Q: A ring and a disk both at rest roll down a hill together. Which rolls slower? A) ring B) disk C) depends on the masses D) both roll at the same speed E) need more information

Q: A coin and a ring roll down an incline at the same time. The one to first reach the bottom is the A) ring. B) coin. C) both reach the bottom at the same time

Q: A flywheel's diameter is twice that of another of the same shape and mass. Rotational inertia of the larger flywheel is A) two times greater. B) four times greater. C) the same as the other's. D) half.

Q: Consider two flywheels of the same size and shape, but one with twice the mass. Rotational inertia of the more massive one is A) two times greater. B) four times greater. C) the same as the other one. D) half.

Q: A tightrope walker more easily balances on a tight wire if her pole A) is held high. B) droops. C) is short but heavy.

Q: Which of these animals has a quicker stride? A) giraffe B) horse C) cat D) mouse

Q: The rotational inertia of a pencil is greatest about an axis A) along its length, where the lead is. B) about its midpoint, like a propeller. C) about its end, like a pendulum.

Q: An industrial flywheel has a greater rotational inertia when most of its mass is A) nearer the rim. B) nearer the axis. C) uniformly spread out as in a disk.

Q: You can swing your legs to and fro more frequently when your legs are A) straight. B) bent. C) same either way

Q: The rotational inertia of your leg is greater when your leg is A) straight. B) bent. C) same either way

Q: Newton's Cradle consists of an aligned row of identical elastic balls suspended by strings so they barely touch one another. When two balls are raised from one end and released, they strike the row and two balls pop out from the other end. If instead, one ball popped out with twice the speed of the two, this would violate A) momentum conservation. B) energy conservation. C) both of these D) none of these

Q: A piece of taffy slams into and sticks to an identical piece of taffy at rest. The momentum of the combined pieces after the collision is the same as before the collision, but this is not true of the kinetic energy, which partly degrades into heat. What percentage of the kinetic energy becomes heat? A) 0% B) 25% C) 50% D) 75% E) need more information

Q: A golf ball is thrown at and bounces backward from a massive bowling ball that is initially at rest. After the collision, compared to the golf ball, the bowling ball has more A) momentum, but less kinetic energy. B) kinetic energy, but less momentum. C) momentum and more kinetic energy. D) need more information

Q: Compared to the recoiling cannon, a fired cannonball has a A) greater momentum. B) greater kinetic energy. C) smaller speed. D) all of the above

Q: Two 2-m/s pool balls roll toward each other and collide. Suppose after bouncing apart each moves at 4 m/s. This collision violates the conservation of A) momentum. B) energy. C) both momentum and energy. D) none of the above

Q: A roller skate at rest may have A) speed. B) velocity. C) momentum. D) energy.

Q: When you and your snowboard are in motion, which of the following can be zero? A) momentum B) kinetic energy C) mass D) inertia E) none of the above

Q: When a cannon is fired, it recoils as the cannonball is set in motion. The cannon and cannonball ideally acquire equal A) but opposite amounts of momentum. B) amounts of kinetic energy. C) both of these D) neither of these

Q: If the speed of a motor scooter doubles, which of the following also doubles? A) momentum B) kinetic energy C) acceleration D) all of the above

Q: If an all-electric car has kinetic energy, then it also must have A) impulse. B) momentum. C) acceleration. D) force. E) none of the above

Q: A moving object has A) speed. B) velocity. C) momentum. D) energy. E) all of these

Q: Impulse involves the time that a force acts, whereas work involves the A) distance that a force acts. B) time and distance that a force acts. C) acceleration that a force produces.

Q: A primary difference between momentum and kinetic energy is A) momenta can cancel; kinetic energy cannot. B) kinetic energy can cancel; momenta cannot. C) either of the above depending on circumstances D) none of the above

Q: Hydrogen, like electricity, is A) an energy source. B) not an energy source. C) a source of both thermal and electric power.

Q: Solar power is commonly used to produce A) heat. B) electricity. C) both of these

Q: Which of these is not a form of solar energy? A) wind energy B) fossil fuel energy C) geothermal energy D) hydroelectric power

Q: The exhaust product from a hydrogen fuel cell is A) carbon dioxide. B) methane. C) pure water. D) nitric acid.

Q: The most concentrated form of energy is A) wind. B) fossil fuel. C) geothermal. D) nuclear.

Q: A machine that promises more energy output than input is A) a fantasy. B) commonplace in today's technology. C) a long-shot worth investing in.

Q: Hydro and wind power are indirect forms of A) solar energy. B) fossil fuels deep down. C) nuclear energy in Earth's interior. D) none of the above

Q: Earth's primary energy source is A) the Sun. B) fossil fuel. C) electricity. D) geothermal.

Q: A car's engine is 20% efficient. When cruising, the car encounters an average retarding force of 1000 N. If the energy content of fuel is 40 megajoules per liter, how many kilometers per liter does the car achieve? A) 8 B) 10 C) 12 D) 14 E) none of the above

Q: A miracle car with a 100% efficient engine burns fuel having a 40-megajoules-per-liter energy content. If air drag and overall frictional forces at highway speeds totals 1000 N, what distance per liter can be achieved on the highway? A) 30 km B) 40 km C) 50 km D) more than 50 km E) need more information

Q: A jack system will increase the potential energy of a heavy load by 1000 J with a work input of 2000 J. The efficiency of the jack system is A) 10%. B) 20%. C) 50%. D) 80%. E) need more information

Q: A machine puts out 100 watts of power for every 1000 watts put into it. The efficiency of the machine is A) 10%. B) 50%. C) 90%. D) 110%. E) none of the above

Q: A hydraulic press has its input piston depressed 20 centimeters while the output piston is raised 1 centimeter. A 1-newton input can lift a load of A) 1 N. B) 10 N. C) 15 N. D) 20 N. E) none of the above

Q: Phil applies 100 N to a pulley system and raises a load one-tenth of his downward pull. Ideally, the weight of the load is A) 100 N. B) 1000 N. C) 10,000 N. D) more than 10,000 N

Q: A hydraulic jack is used to lift objects such as automobiles. If the input force is 200 N over a distance of 1 meter, the output force over a distance of 0.1 meter is ideally A) 200 N. B) 500 N. C) 1000 N. D) 2000 N. E) none of the above

Q: When properly used, a hydraulic press, like a wheel and axle, is capable of multiplying force input. A) A true statement. B) A false statement. C) Yes, and in special cases, energy as well.

Q: A hydraulic press, like an inclined plane, is capable of increasing energy. A) sometimes true B) always false C) always true D) sometimes false

Q: A common pulley acts similar to a A) hydraulic press. B) gear. C) common lever. D) tension producer.

Q: Although perpetual motion is the natural order of things in the universe A) it follows that machines can operate and do work by perpetual motion. B) no perpetual-motion device that multiplies energy exists. C) both of these are false statements

Q: A 1-kg ball dropped from 2 m rebounds only 1.5 m after hitting the ground. The amount of energy converted to heat is about A) 0.5 J. B) 1.0 J. C) 1.5 J. D) 2.0 J. E) more than 2.0 J.

Q: Acrobat Bart at the circus drops vertically onto the end of a see-saw, with his partner Art equidistant from the fulcrum at the other end. Art is propelled straight upward a distance twice that of Bart's dropping distance. Neglecting inefficiencies we see A) the masses of Art and Bart are equal. B) Art has half the mass of Bart. C) need more information

Q: A circus diver drops from a high pole into water far below. When he is halfway down A) his potential energy is halved. B) he has gained an amount of kinetic energy equal to half his initial potential energy. C) his kinetic energy and potential energy are equal. D) all of the above E) none of the above