Q&A Hero

Q: A 2-kg block is thrown upward from a point 20 m above the Earth's surface. At what height above Earth's surface will the gravitational potential energy of the Earth-block system have increased by 500 J? A) 5 m B) 25 m C) 46 m D) 70 m E) 270 m

Q: A golf ball is struck by a golf club and falls on a green eight feet above the tee. The potential energy of the Earth-ball system is greatest: A) just before the ball is struck B) just after the ball is struck C) just after the ball lands on the green D) when the ball comes to rest on the green E) when the ball reaches the highest point in its flight

Q: A force on a particle is conservative if: A) its work equals the change in the kinetic energy of the particle B) it obeys Newton's second law C) it obeys Newton's third law D) its work depends on the end points of the motion, not this the path between E) it is not a frictional force

Q: Only if a force on a particle is conservative: A) does it do no work when the particle moves exactly once around any closed path B) does the work it does equal the change in the kinetic energy of the particle C) does it obey Newton's second law D) does it obey Newton's third law E) it is not a frictional force

Q: Two objects interact with each other and with no other objects. Initially object A has a speed of 5 m/s and object B has a speed of 10 m/s. In the course of their motion they return to their initial positions. Then A has a speed of 4 m/s and B has a speed of 7 m/s. We can conclude: A) the potential energy changed from the beginning to the end of the trip B) mechanical energy was increased by nonconservative forces C) mechanical energy was decreased by nonconservative forces D) mechanical energy was increased by conservative forces E) mechanical energy was decreased by conservative forces

Q: Two particles interact by conservative forces. In addition, an external force acts on each particle. They complete round trips, ending at the points where they started. Which of the following must have the same values at the beginning and end of this trip? A) a total kinetic energy of the two-particle system B) the potential energy of the two-particle system C) the mechanical energy of the two-particle system D) the total linear momentum of the two-particle system E) none of the above

Q: A nonconservative force: A) violates Newton's second law B) violates Newton's third law C) cannot do any work D) must be perpendicular to the velocity of the particle on which it acts E) none of the above

Q: Suppose that the fundamental dimensions are taken to be: force (F), velocity (V) and time (T). The dimensions of potential energy are then: A) F/T B) FVT C) FV/T D) F/T2 E) FV2/T2

Q: Which one of the following five quantities CANNOT be used as a unit of potential energy?A) watt.secondB) gram.cm/s2C) jouleD) kg.m2/s2E) ft.lb

Q: A body at rest in a system is capable of doing work if: A) the potential energy of the system is positive B) the potential energy of the system is is negative C) it is free to move in such a way as to decrease its kinetic energy D) it is free to move in such a way as to decrease the potential energy of the system E) it is free to move in such a way as to increase the potential energy of the system

Q: The wound spring of a clock possesses: A) kinetic but no potential energy B) potential but no kinetic energy C) both potential and kinetic energy in equal amounts D) neither potential nor kinetic energy E) both potential and kinetic energy, but more kinetic energy than potential energy

Q: No kinetic energy is possessed by: A) a shooting star B) a rotating propeller on a moving airplane C) a pendulum at the bottom of its swing D) an elevator standing at the fifth floor E) a cyclone

Q: A good example of kinetic energy is provided by: A) a wound-up clock spring B) the raised weights of a grandfather's clock C) a tornado D) a gallon of gasoline E) an automobile storage battery

Q: Which of the following is NOT a correct unit for work?A) ergB) ft-lbC) wattD) newton-meterE) joule

Q: Which of the following is the correct combination of dimensions for energy? A) MLT B) LT2 /M C) ML2/T2 D) M2L3T E) ML/T2

Q: The weight of an object on the moon is one-sixth of its weight on the Earth. The ratio of the kinetic energy of a body on the Earth moving with speed Vto that of the same body moving with speed Von the moon is: A) 6:1 B) 36:1 C) 1:1 D) 1:6 E) 1:36

Q: An object is constrained by a cord to move in a circular path of radius 0.5m on a horizontal frictionless surface. The cord will break if its tension exceeds 16N. The maximum kinetic energy the object can have is: A) 4 J B) 8 J C) 16 J D) 32 J E) 64 J

Q: An 8000-N car is traveling at 12 m/s along a horizontal road when the brakes are applied. The car skids to a stop in 4.0 s. How much kinetic energy does the car lose in this time?A) 4.8 x104JB) 5.9 x104JC) 1.2 x105JD) 5.8 x105JE) 4.8 x106J

Q: Two trailers, X with mass 500 kg and Y with mass 2000 kg, are being pulled at the same speed. The ratio of the kinetic energy of Y to that of X is: A) 1:1 B) 2:1 C) 4:1 D) 9:1 E) 1500:1

Q: Which of the following bodies has the largest kinetic energy? A) Mass 3Mand speed V B) Mass 3Mand speed 2V C) Mass 2Mand speed 3V D) Mass Mand speed 4V E) All four of the above have the same kinetic energy

Q: A mass of 47 kg is moving horizontally as a force of 190 N, directed at 25 below the horizontal, is exerted on it. When its speed is 7.3 m/s, what is the rate at which the force is doing work? A) 0 W B) 340 W C) 590 W D) 1300 W E) 1400 W

Q: A force = (4.1 N) + (2.6 N) - (4.7 N) acts on a mass of 2.3 kg as it moves in the xdirection at a speed of 7.2 m/s. What is the rate at which the force is doing work?A) 8.8 WB) 16 WC) 30 WD) 49 WE) 60 W

Q: A particle starts from rest and is acted on by a net force that does work at a rate that is proportional to the time t. The speed of the particle is proportional to: A) B) t C) t2 D) 1/ E) 1/t

Q: A kilowatt hour is a unit of: A) power B) energy/time C) energy D) power/time E) force/distance

Q: A watt per hour is a unit of: A) energy B) power C) force D) acceleration E) none of these

Q: A watt second is a unit of: A) force B) power C) displacement D) speed E) energy

Q: Which of the following five quantities is NOT an expression for energy? Here mis a mass, gis the acceleration due to gravity, hand dare distances, Fis a force, vis a speed, ais an acceleration, Pis power, and tis time. A) mgh B) Fd C) 1/2mv2 D) ma E) Pt

Q: Which of the following five units represents a quantity that is NOT the same type as the other four? A) joule B) erg C) watt D) footpound E) newtonmeter

Q: A 50-N force is the only force on a 2-kg crate that starts from rest. At the instant the crate has gone 2 m the rate at which the force is doing work is: A) 2.5 W B) 25 W C) 75 W D) 100 W E) 500 W

Q: A 50-N force acts on a 2-kg crate that starts from rest. When the force has been acting for 2 s the rate at which it is doing work is: A) 100 W B) 1000 W C) 2500 W D) 5000 W E) 63000 W

Q: A person holds an 80-N weight 2 m above the floor for 30 seconds. The power required to do this is: A) 5.3 W B) 40 W C) 80 W D) 160 W E) none of these

Q: An escalator is used to move 20 people (60 kg each) per minute from the first floor of a department store to the second floor, 5 m above. The power required is approximately: A) 100 W B) 200 W C) 1000 W D) 2000 W E) 60,000 W

Q: Power has the dimensions of: A) ML2/T2 B) MT/L2 C) ML/T2 D) ML2/T3 E) none of these

Q: One watt is:A) 1 kg -m/s3B) 1 kg -m2/sC) 1 kg -m2/s3D) 1 kg -m/sE) 1 kg -m2/s2

Q: A particle moving along the xaxis is acted upon by a single force F= F0e-kx, where F0and kare constants. The particle is released from rest at x= 0. It will attain a maximum kinetic energy of:A) F0/kB) F0/ekC) kF0D) 1/2(kF0)2E) kekF0

Q: The plot shows the force on an object as it moves from x= 0 m to x= 20 m. How much work is done on the object? A) 40 J B) 90 J C) 200 J D) 450 J E) 750 J

Q: When a certain rubber band is stretched a distance x, it exerts a restoring force F= ax+ bx2, where aand bare constants. The work done in stretching this rubber band from x= 0 to x= Lis: A) aL2+ bLx3 B) aL+ 2bL2 C) a+ 2bL D) bL E) aL2/2 + bL3/3

Q: A 1.5 kg crate falls from a height of 2.0 m onto an industrial spring scale with a spring constant of 1.5 x105N/m. At its greatest compression the reading on the scale is:A) 15 NB) 29 NC) 1.5 x103ND) 2.1x103NE) 3.0 x103N

Q: A 2-kg block is attached to a horizontal ideal spring with a spring constant of 200 N/m. When the spring has its equilibrium length the block is given a speed of 5 m/s. What is the maximum elongation of the spring? A) 0 m B) 0.5 m C) 5 m D) 10 m E) 100 m

Q: In the plot shown of force vs. distance, approximately how much work is done in moving an object from x= 5 m to x= 15 m? A) 10 J B) 55 J C) 125 J D) 275 J E) cannot be calculated without knowing the mass of the object

Q: When a certain rubber band is stretched a distance x, it exerts a restoring force of magnitude F= Ax, where Ais a constant. The work done by a person in stretching this rubber band from x= 0 to x= Lis: A) AL2 B) AL C) A+ 2L2 D) A/L E) AL2/2

Q: An ideal spring is hung vertically from the ceiling. When a 2.0-kg mass hangs at rest from it, the spring is extended 6.0 cm from its relaxed length. An upward external force is then applied to the block to move it upward a distance of 16 cm. While the block is being raised by the force, the work done by the spring isA) -1.0 JB) -0.52 JC) -0.26 JD) 0.52 JE) 1.0 J

Q: Three identical springs (X,Y,Z) are arranged as shown. When a 4.0-kg mass is hung on X, the mass descends 3.0 cm. When a 6.0-kg mass is hung on Y, the mass descends: A) 2.0 cm B) 4.0 cm C) 4.5 cm D) 6.0 cm E) 9.0 cm

Q: An ideal spring is hung vertically from the ceiling. When a 2.0-kg mass hangs at rest from it, the spring is extended 6.0 cm from its relaxed length. A downward external force is now applied to the mass to extend the spring an additional 10 cm. While the spring is being extended by the force, the work done by the spring is:A) -3.6 JB) -3.3 JC) -1.0 JD) 3.3 JE) 3.6 J

Q: This plot shows an object being moved by a series of forces. Which segments of the motion could have been caused by fixed springs? A) None of the segments could represent work being done by springs. B) Any of the segments could represent work being done by springs. C) Segments A and C only. D) Segments B and D only. E) Segment A only.

Q: A spring of spring constant kis attached to a block of mass m. The spring moves the block through a displacement x. How can you calculate how much work the spring does on the block? A) Multiply the spring force, kx, by the distance x. B) Multiply the spring force, kx2, by the distance x. C) Integrate the spring force, kx, over the distance x. D) Integrate the spring force, kx2, over the time it takes the block to move. E) You cannot calculate this without knowing the acceleration of the block.

Q: An ideal spring, with a pointer attached to its end, hangs next to a scale. With a 100-N weight attached, the pointer indicates "40" on the scale as shown. Using a 200-N weight instead results in "60" on the scale. Using an unknown weight X instead results in "30" on the scale. The weight of X is: A) 20 N B) 30 N C) 40 N D) 50 N E) 75 N

Q: A block is attached to the end of an ideal spring and moved from coordinate xito coordinate xf. The relaxed position is at x= 0. The work done by spring is positive if:A) xi= 2 cm and xf= 4 cmB) xi= -2 cm and xf= 4 cmC) xi= -2 cm and xf= -4 cmD) xi= 2 cm and xf= -4 cmE) xi= -4 cm and xf= -2 cm

Q: A baseball is hit high into the upper bleachers of left field. Over its entire flight the work done by gravity and the work done by air resistance, respectively, are: A) positive; positive B) positive; negative C) negative; positive D) negative; negative E) unknown since vital information is lacking

Q: A line drive to the shortstop is caught at the same height as it was originally hit. Over its entire flight the work done by gravity and the work done by air resistance, respectively, are: A) zero; positive B) zero; negative C) positive; negative D) negative; positive E) negative; negative

Q: A woman lifts a barbell 2.0 m in 5.0 s. If she lifts it the same distance in 10 s, the work done by her is: A) four times as great B) two times as great C) the same D) half as great E) one-fourth as great

Q: A man moves the 10-g object shown in a vertical plane at a constant speed from position X to position Y along a circular track of radius 20 m. The process takes 0.75 min. The work done by the man is about: A) 1 J B) 2 J C) 4 J D) 6 J E) 12 J

Q: A man pushes an 80-N crate a distance of 5.0 m upward along a frictionless slope that makes an angle of 30°with the horizontal. The force he exerts is parallel to the slope. If the speed of the crate is constant, then the work done by the man is:A) -200 JB) 61 JC) 140 JD) 200 JE) 260 J

Q: A man pushes an 80-N crate a distance of 5.0 m upward along a frictionless slope that makes an angle of 30°with the horizontal. His force is parallel to the slope. If the speed of the crate decreases at a rate of 1.5 m/s2, then the work done by the man is:A) -200 JB) 61 JC) 140 JD) 200 JE) 400 J

Q: A man pulls a 100-N crate up a frictionless 30°slope 5 m high as shown. Assuming that the crate moves at constant speed, the work done by the man is:A) -500 JB) -250 JC) 0 JD) 250 JE) 500 J

Q: The work done by gravity during the descent of a projectile is: A) positive B) negative C) zero D) depends for its sign on the direction of the yaxis E) depends for its sign on the direction of both the xand yaxes

Q: A 1-kg block is lifted vertically 1 m at constant speed by a boy. The work done by the boy is about:A) 1 ft-lbB) 1 JC) 10 JD) 0.1 JE) 0 J

Q: An 80-N crate slides with constant speed a distance of 5.0 m downward along a rough slope that makes an angle of 30ï‚°with the horizontal. The work done by the force of gravity is:A) -400 JB) -200 JC) -69 JD) 200 JE) 400 J

Q: A 0.50-kg object moves on a horizontal frictionless circular track with a radius of 2.5 m. An external force of 3.0 N, always tangent to the track, causes the object to speed up as it goes around. If it starts from rest, then at the end of one revolution the radial component of the force of the track on it is: A) 19 N B) 38 N C) 47 N D) 75 N E) 96 N

Q: A 0.50-kg object moves in a horizontal circular track with a radius of 2.5 m. An external force of 3.0 N, always tangent to the track, causes the object to speed up as it goes around. If it starts from rest its speed at the end of one revolution is: A) 5.5 m/s B) 14 m/s C) 15 m/s D) 18 m/s E) 21 m/s

Q: A Boston Red Sox baseball player catches a ball of mass mthat is moving toward him with speed v. While bringing the ball to rest, his hand moves back a distance d. Assuming constant deceleration, the horizontal force exerted on the ball by his hand is: A) mv/d B) mvd C) mv2/d D) 2mv/d E) mv2/(2d)

Q: A 4-kg cart starts up an incline with a speed of 3 m/s and comes to rest 2 m up the incline. The total work done on the cart is:A) -6 JB) -8 JC) -12 JD) -18 JE) impossible to calculate without more information

Q: A 5.0-kg cart is moving horizontally at 6.0 m/s. In order to change its speed to 10.0 m/s, the net work done on the cart must be: A) 20 J B) 40 J C) 90 J D) 160 J E) 400 J

Q: The amount of work required to stop a moving object is equal to the: A) velocity of the object B) kinetic energy of the object C) mass of the object times its acceleration D) mass of the object times its velocity E) square of the velocity of the object

Q: The velocity of a particle moving along the x axis changes from vito vf. For which values of viand vfis the total work done on the particle positive?A) vi= 5m/s, vf= 2m/sB) vi= 5m/s, vf= -2m/sC) vi= -5m/s, vf= -2m/sD) vi= -5m/s, vf= 2m/sE) vi= -2m/s, vf= -5m/s

Q: A particle starts from rest at time t= 0 and moves along the xaxis. If the net force on it is proportional to t, its kinetic energy is proportional to: A) t B) t2 C) t4 D) 1/t2 E) none of the above

Q: At time t= 0 a 2-kg particle has a velocity of (4 m/s) - (3 m/s). At t= 3 s its velocity is (2 m/s) + (3 m/s). During this time the work done on it was:A) 4 JB) -4 JC) -12 JD) -40 JE) (4 J) + (36 J)

Q: At time t= 0 a particle starts moving along the xaxis. If its kinetic energy increases uniformly with tthe net force acting on it must be: A) constant B) proportional to t C) inversely proportional to t D) proportional to E) proportional to 1/

Q: Two objects with masses, m1and m2, have the same kinetic energy and are both moving to the right. The same constant force is applied to the left to both masses. If m1= 4m2, the ratio of the stopping distance of m1to that of m2is: A) 1:4 B) 4:1 C) 1:2 D) 2:1 E) 1:1

Q: In raising an object to a given height by means of an inclined plane, as compared with raising the object vertically, there is a reduction in: A) work required B) distance pushed C) friction D) force required E) value of the acceleration due to gravity

Q: The mechanical advantage of any machine is: A) the efficiency of the machine B) the work done by the machine C) the ratio of the work done by the machine to the work expended on it D) the ratio of the force exerted by the machine to the force applied to it E) the ratio of the force applied to the machine to the force exerted by it

Q: An 8-N block slides down an incline. It has an initial speed of 7 m/s. The work done by the resultant force on this block is: A) 20 J B) 28 J C) 56 J D) impossible to calculate without more information E) none of these

Q: A 100-kg piano rolls down a 20 incline. A man tries to keep it from accelerating, and manages to keep its acceleration to 1.2 m/s2. If the piano rolls 5 m, what is the net work done on it by all the forces acting on it? A) 60 J B) 100 J C) 600 J D) 1000 J E) 4900 J

Q: A man pulls a sled along a rough horizontal surface by applying a constant force at an angle above the horizontal. In pulling the sled a horizontal distance d, the work done by the man is:A) FdB) FdcosC) Fdsin D) Fd/cosE) Fd/sin

Q: A particle moves 5 m in the positive xdirection while being acted upon by a constant force= (4 N) + (2 N) - (4 N). The work done on the particle by this force is:A) 20 JB) 10 JC) -20 JD) 30 JE) is impossible to calculate without knowing other forces

Q: An object of mass 1 kg is whirled in a horizontal circle of radius 0.5 m at a constant speed of 2 m/s. The work done on the object during one revolution is: A) 0 J B) 1 J C) 2 J D) 4 J E) 16 J

Q: An object moves in a circle at constant speed. The work done by the centripetal force is zero because: A) the displacement for each revolution is zero B) the average force for each revolution is zero C) there is no friction D) the magnitude of the acceleration is zero E) the centripetal force is perpendicular to the velocity

Q: A crate is initially at rest on a horizontal frictionless table. A constant horizontal force F is applied. Which of the following five graphs is a correct plot of work W as a function of crate speed v? A) I B) II C) III D) IV E) V

Q: A 0.50-kg object moves in a horizontal circular track with a radius of 2.5 m. An external force of 3.0 N, always tangent to the track, causes the object to speed up as it goes around. The work done by the external force as the mass makes one revolution is: A) 7.5 J B) 24 J C) 47 J D) 94 J E) 120 J

Q: Camping equipment weighing 6000 N is pulled across a frozen lake by means of a horizontal rope. The coefficient of kinetic friction is 0.05. How much work is done by the campers in pulling the equipment 1000 m if its speed is increasing at the constant rate of 0.20 m/s2?A) -1.2 x106JB) 1.2x105JC) 3.0 x105JD) 4.2 x105JE) 4.1x106J