MCQ WPE

Energy Conservation With Conservative Forces: Two identical grasshoppers jump into the air with the same initial speed and experience no air resistance. Grasshopper A goes straight up, but grasshopper B goes up at a 66° angle above the horizontal. Which of the following statements about these grasshoppers are correct?

- At their highest point, grasshopper B is moving faster than grasshopper A. - At their highest point, grasshopper A has more gravitational potential energy than grasshopper B. - At their highest point, both of them have the same amount of mechanical energy.

Energy Conservation With Conservative Forces: A 1-kg ball is released from a height of 6 m, and a 2-kg ball is released from a height of 3 m. Air resistance is negligible as they fall. Which of the following statements about these balls are correct? (There could be more than one correct choice.)

- Both balls will reach the ground with the same kinetic energy. -As they reach the ground, the 1-kg ball will be moving faster than the 2-kg ball.

Energy Conservation With Nonconservative Forces: A heavy sled and a light sled, both moving horizontally with the same speed, suddenly slide onto a rough patch of snow and eventually come to a stop. The coefficient of kinetic friction between the sleds and the rough snow is the same for both of them. Which of the following statements about these sleds are correct? (There could be more than one correct choice.) Check all that apply.

- The friction from the snow will do more negative work on the heavy sled than on the light sled. - Both sleds will slide the same distance on the rough snow before stopping.

Energy Conservation With Nonconservative Forces: A heavy sled and a light sled, both moving horizontally with the same kinetic energy, suddenly slide onto a rough patch of snow and eventually come to a stop. The coefficient of kinetic friction between the sleds and the rough snow is the same for both of them. Which of the following statements about these sleds are correct? (There could be more than one correct choice.)

- The friction from the snow will do the same amount of work on both sleds. - On the rough snow, the change in kinetic energy will be the same for both sleds. -The light sled will slide farther on the rough snow than the heavy sled.

Energy Conservation With Conservative Forces: A heavy dart and a light dart are launched vertically by identical ideal springs. Both springs were initially compressed by the same amount. There is no significant air resistance. Which of the following statements about these darts are correct? (There could be more than one correct choice.)

- The light dart goes higher than the heavy dart. - at max H same GPE

Energy Conservation With Conservative Forces: A heavy frog and a light frog jump straight up into the air. They push off in such away that they both have the same kinetic energy just as they leave the ground. Air resistance is negligible. Which of the following statements about these frogs are correct? (There could be more than one correct choice.) Check all that apply.

- The lighter frog goes higher than the heavier frog. - Just as they leave the ground, the lighter frog is moving faster than the heavier frog.

Energy Conservation With Nonconservative Forces: As shown in the figure, a 1.45-kg block is held in place against the spring by a 21-N horizontal external force. The external force is removed, and the block is projected with a velocity v1 = 1.2 m/s as it separates from the spring. The block descends a ramp and has a velocity v2 = 2.1 m/s at the bottom. The track is frictionless between points A and B. The block enters a rough section at B, extending to E. The coefficient of kinetic friction between the block and the rough surface is 0.29. The velocity of the block is v3 = 1.4 m/s at C. The block moves on to D, where it stops. How much work is done by friction between points B and C?

-1.8

Work: A 30-N box is pulled upward 6.0 m along the surface of a ramp that rises at 37° above the horizontal. How much work does gravity do on the box during this process? -140 J120 J-1100 J-180 J-110 J

-110

Work: A person carries a 2.00-N pebble through the path shown in the figure, starting at point A and ending at point B. The total time from A to B is 6.75 min. How much work did gravity do on the rock between A and B?

-30J

Work-Energy Theorem: A driver, traveling at 22 m/s, slows down her 2000 kg truck to stop for a red light. What work is done on the truck by the friction force of the road? -4.4 × 104 J-9.7 × 10^5 J-2.2 × 104 J-4.8 × 10^5 J

-4.8 × 10^5 J

Springs: An ideal spring has a spring constant (force constant) of 60 N/m. How much energy does it store when it is stretched by 1.0 cm? 600 J60 J0.0030 J0.30 J

.0030

Springs: An ideal spring with a force constant (spring constant) of 15 N/m is initially compressed by 3.0 cm from its uncompressed position. How much work is required to compress the spring an additional 4.0 cm? 0.012 J0.0068 J0.024 J0.030 J

.030

Work-Energy Theorem: A stone initially moving at 8.0 m/s on a level surface comes to rest due to friction after it travels 11 m. What is the coefficient of kinetic friction between the stone and the surface?

.30

Energy Conservation With Nonconservative Forces: A 0.46-kg block is held in place against the spring by a 30-N horizontal external force. The external force is removed, and the block is projected with a velocity v1 = 1.2 m/s upon separation from the spring, as shown in the figure. The block descends a ramp and has a velocity v2 = 1.5 m/s at the bottom. The track is frictionless between points A and B. The block enters a rough section at point B, extending to E. The coefficient of kinetic friction between the block and the rough surface is 0.38. The velocity of the block is v3 = 1.4 m/s at point C. The block moves on to D, where it stops. What distance does the block travel between points B and D?

.30m

Energy Conservation With Nonconservative Forces: On a planet where g = 10.0 m/s2 and air resistance is negligible, a sled is at rest on a rough inclined hill rising at 30° as shown in the figure. The object is allowed to move and it stops on a rough horizontal surface, at a distance of 4.0 m from the bott

.31

Work: It requires 0.30 kJ of work to fully drive a stake into the ground. If the average resistive force on the stake by the ground is 828 N, how long is the stake? 0.23 m0.32 m0.36 m0.41 m

.36m

Springs: How much work is required to stretch an ideal spring of spring constant (force constant) 40 N/m from x = 0.20 m to x = 0.25 m if the unstretched position is at x = 0.00 m?

.45j

Energy Conservation With Nonconservative Forces: A 0.12-kg block is held in place against the spring by a 35-N horizontal external force. The external force is removed, and the block is projected with a velocity v 1 = 1.2 m/s when it separates from the spring, as shown in the figure. The block descends a ramp and has a velocity v 2 = 1.4 m/s at the bottom of the ramp. The track is frictionless between points A and B. The block enters a rough section at B, extending to E. The coefficient of kinetic friction between the block and the rough surface is 0.26. The block moves on to D, where it stops. By how many centimeters was the spring initially compressed?

.49cm

Kinetic Energy: A 1.0-kg object moving in a certain direction has a kinetic energy of 2.0 J. It hits a wall and comes back with half its original speed. What is the kinetic energy of this object at this point? 4.0 J0.50 J1.0 J2.0 J0.25 J

.50J

Energy Conservation With Conservative Forces: A 1500-kg car moving at 25 m/s hits an initially uncompressed horizontal ideal spring with spring constant (force constant) of 2.0 × 106 N/m. What is the maximum distance the spring compresses

.68

Power: If electricity costs 7.06¢/kW∙h, how much would it cost you to run a 120-W stereo system 4.0 hours per day for 4.0 weeks? $2.66$1.62$0.14$0.95

.95

Work: A person carries a 25.0-N rock through the path shown in the figure, starting at point A and ending at point B. The total time from A to B is 1.50 min. How much work did gravity do on the rock between A and B?

0

Work: A stone with a mass of 1.0 kg is tied to the end of a light string which keeps it moving in a circle with a constant speed of 4.0 m/s on a perfectly smooth horizontal tabletop. The radius of the path is 0.60 m. How much work does the tension in the string do on the stone as it makes one-half of a complete circle? 3.8 J0 J80 J40 J100 J

0

Work: You carry a 7.0-kg bag of groceries 1.2 m above the ground at constant speed across a 2.7 m room. How much work do you do on the bag in the process?

0

Work: A 35-N bucket of water is lifted vertically 3.0 m and then returned to its original position. How much work did gravity do on the bucket during this process?

0J

Graphical Interpretation of Work: The resultant force on an object over a 0.50-s time interval is plotted in the graph in the figure. How much work did this force do on the object during the 0.50-s interval?

0j

Kinetic Energy: What is the minimum energy needed to change the speed of a 1600-kg sport utility vehicle from 15.0 m/s to 40.0 m/s? 40.0 kJ0.960 MJ1.10 MJ10.0 kJ20.0 kJ

1.10

ower: A certain battery charger uses 12 W of power. At 6.0 cents per kilowatt-hour, how much does it cost to charge batteries for a full day? 28¢75¢1.7¢2.3¢1.4¢

1.7

Kinetic Energy: An object hits a wall and bounces back with half of its original speed. What is the ratio of the final kinetic energy to the initial kinetic energy of the object? 1/161/21/41/8

1/4

Energy Conservation With Conservative Forces: A block slides down a frictionless inclined ramp and experiences no significant air resistance. If the ramp angle is 17.0° above the horizontal and the length of the surface of the ramp is 20.0 m, find the speed of the block as it reaches the bottom of the ramp, assuming it started sliding from rest at the top.

10.7

Energy Conservation With Conservative Forces: A small but dense 2.0-kg stone is attached to one end of a very light rod that is 1.2 m long. The other end of the rod is attached to a frictionless pivot. The rod is raised until it is vertical, with the stone above the pivot. The rod is released and the stone moves in a vertical circle with no air resistance. What is the tension in the rod as the stone moves through the bottom of the circle? 40 N20 N80 N60 N100 N

100n

Energy Conservation With Conservative Forces: A toy rocket that weighs 10 N blasts straight up from ground level with an initial kinetic energy of 40 J. At the exact top of its trajectory, its total mechanical energy is 140 J. To what vertical height above the ground does it rise, assuming no air resistance? 10 m14 m24 m1.0 m

10m

Work-Energy Theorem: A 10-kg dog is running with a speed of 5.0 m/s. What is the minimum work required to stop the dog in 2.40 s? 75 J50 J125 J100 J

125

Graphical Interpretation of Work: A force acts on an object, causing it to move parallel to the force. The graph in the figure shows this force as a function of the position of the object. How much work does the force do as the object moves from 0 to 15 m?

125J

Power: A force produces power P by doing work W in a time T. What power will be produced by a force that does six times as much work in half as much time? P1616 P112112 P12P6P

12p

Energy Conservation With Conservative Forces: In a museum exhibit of a simple pendulum, a very small but dense 6.0-kg ball swings from a very light 2.5-m wire. The ball is released from rest when the pendulum wire makes a 65° angle with the vertical, and it swings in a circular arc with no appreciable friction or air resistance. What is the tension in the wire just as the ball swings through its lowest position?

130

Work-Energy Theorem: In a ballistics test, a 28-g bullet pierces a sand bag that is 30 cm thick. If the initial bullet velocity was 55 m/s and it emerged from the sandbag moving at 18 m/s what was the magnitude of the friction force (assuming it to be constant) that the bullet experienced while it traveled through the bag? 13 N38 N1.3 N130 N

130

Energy Conservation With Conservative Forces: A roller coaster starts from rest at a height h at the left side of a loop-the-loop, as shown in the figure. It is not attached to the track in anyway, and there is no friction from the track or from air resistance. If the radius of the loop is R = 6.0 m, what is the minimum height h for which the roller coaster will not fall off the track at the top of the loop? 12 m18 m15 m21 m8.5 m

15

Gravitational Potential Energy: You do 116 J of work while pulling your sister back on a frictionless swing, whose chain is 5.10 m long, until the swing makes an angle of 32.0° with the vertical. What is your sister's mass? 17.6 kg13.0 kg15.3 kg19.0 kg

15.3kg

Energy Conservation With Conservative Forces: A 60-kg skier pushes off the top of a frictionless hill with an initial speed of 4.0 m/s. How fast will she be moving after dropping 10 m in elevation? Air resistance is negligible. 15 m/s0.15 km/s10 m/s0.20 km/s49 m/s

15m/s

Work-Energy Theorem: A 100-N force has a horizontal component of 80 N and a vertical component of 60 N. The force is applied to a cart on a level frictionless floor. The cart starts from rest and moves 2.0 m horizontally along the floor due to this force. What is the cart's final kinetic energy? 160 Jzero200 J120 J

160j

Power: A child pulls on a wagon with a force of 75 N. If the wagon moves a total of 42 m in 3.1 min, what is the average power delivered by the child? 21 W17 W22 W26 W

17

Gravitational Potential Energy: A tennis ball bounces on the floor three times, and each time it loses 23.0% of its energy due to heating. How high does it bounce after the third time, if we released it 4.0 m from the floor? 18 cm180 cm180 mm240 cm

180

Work: Find the net work done by friction on a box that moves in a complete circle of radius 1.82 m on a uniform horizontal floor. The coefficient of kinetic friction between the floor and the box is 0.25, and the box weighs 65.0 N. 0 J190 J1800 J370 J

190

Springs: An ideal spring stretches by 21.0 cm when a 135-N object is hung from it. If instead you hang a fish from this spring, what is the weight of a fish that would stretch the spring by 31.0 cm? 145 N91 N279 N199 N

199

Springs: An ideal spring has a spring constant (force constant) of 2500 N/m. is stretched 4.0 cm. How much work is required to stretch the spring by 4.0 cm?

2

Energy Conservation With Conservative Forces: A stone is released from rest at a height hh at the left side of a loop-the-loop, as shown in the figure. There is no appreciable friction from the track or from air resistance. If the radius of the loop is RR, what is the minimum height hh for which the stone will not fall off the track at the top of the loop?

2.5r

Power: The net force that an animal exerts on a large fruit it has found is observed over a 10-s interval and is shown in the graph in the figure. What was the average power delivered to the fruit by the animal over this time interval?

2.5w

Power: How many joules of energy are used by a 1.0-hp motor that runs for 1.0 hour? (1 hp = 746 W)

2.7MJ

Energy Conservation With Conservative Forces: A 5.0-N projectile leaves the ground with a kinetic energy of 220 J. At the highest point in its trajectory, its kinetic energy is 120 J. To what vertical height, relative to its launch point, did it rise if there was no air resistance?

20

Energy Conservation With Conservative Forces: Assuming negligible friction, what spring constant (force constant) would be needed by the spring in a "B-B gun" to fire a 10-g pellet to a height of 100 m if the spring is initially compressed by 0.10 m? 200 N/m2000 N/cm20 N/m0.0020 N/m20 N/cm

20

Energy Conservation With Nonconservative Forces: An object with a mass of 10 kg is initially at rest at the top of a frictionless inclined plane that rises at 30° above the horizontal. At the top, the object is initially 8.0 m from the bottom of the incline, as shown in the figure. When the object is released from this position, it eventually stops at a distance d from the bottom of the inclined plane along a horizontal surface, as shown. The coefficient of kinetic friction between the horizontal surface and the object is 0.20, and air resistance is negligible. Find the distance d.

20

Graphical Interpretation of Work: A force acts on an object, causing it to move parallel to the force. The graph in the figure shows this force as a function of the position of the object. How much work does the force do as the object moves from 0 m to 4 m?

20

Graphical Interpretation of Work: A force acts on an object, causing it to move parallel to the force. The graph in the figure shows this force as a function of the position of the object. How much work does the force do as the object moves from 4 m to 6 m?

20

Energy Conservation With Conservative Forces: The figure shows a famous roller coaster ride. You can ignore friction. If the roller coaster leaves point Q from rest, what is its speed at the top of the 25-m peak (point S)

22

Graphical Interpretation of Work: The net force that an animal exerts on a large piece of fruit it has found is observed and is shown in the graph in the figure. If the force is parallel to the motion of the fruit, how much work did the animal do during the encounter?

25

Power: A 1321-kg car climbs a 5.0° slope at a constant speed of 80.0 km/h. Assuming that air resistance may be neglected, at what rate (in kW) must the engine deliver energy to the drive wheels of the car?

25

Work-Energy Theorem: How large a net force is required to accelerate a 1600-kg SUV from rest to a speed of 25 m/s in a distance of 200 m? 0 N200 N1600 N400 N2500 N

2500

Work-Energy Theorem: The horizontal force that an animal exerts on a large fruit it has found is observed and is shown in the graph in the figure. If the fruit was initially sliding on the frictionless ground at 5.5 cm/s when the animal first grabbed it, by how much did the animal change its kinetic energy during this encounter?

25j

Springs: It takes 87 J of work to stretch an ideal spring from 1.4 m to 2.9 m from equilibrium. What is the value of the spring constant (force constant) of this spring?

27

Power: What is the net power needed to change the speed of a 1600-kg sport utility vehicle from 15.0 m/s to 40.0 m/s in 4.00 seconds? 14.0 kW140 kW10.0 kW275 kW100 kW

275

Work-Energy Theorem: A certain car traveling at 34.0 mph skids to a stop in 29 meters from the point where the brakes were applied. In approximately what distance would the car have stopped had it been going 105.4 mph? 29 m90 m279 m158 m51 m

279

Energy Conservation With Nonconservative Forces: A 60-kg skier starts from rest from the top of a 50-m high slope. If the work done by friction is -6.0 kJ, what is the speed of the skier on reaching the bottom of the slope?

28

Work-Energy Theorem: When a car of mass 1167 kg accelerates from 10.0 m/s to some final speed, 4.00 × 105 J of work are done. Find this final speed. 30.8 m/s28.0 m/s25.2 m/s22.4 m/s

28

Kinetic Energy: How much kinetic energy does a 0.30-kg stone have if it is thrown at 44 m/s? 510 J290 J580 J440 J

290

Energy Conservation With Conservative Forces: When you drop a pebble from height HH, it reaches the ground with kinetic energy KK if there is no air resistance. From what height should you drop it so it will reach the ground with twice as much kinetic energy?

2H

Work-Energy Theorem: How much work must be done by frictional forces in slowing a 1000-kg car from 26.1 m/s to rest? 2.73 × 10^5 J3.41 × 10^5 J4.77 × 10^5 J4.09 × 10^5 J

3.41 × 10^5 J

Graphical Interpretation of Work: A force acts on an object, causing it to move parallel to the force. The graph in the figure shows this force as a function of the position of the object. How much work does the force do as the object moves from 6 m to 12 m?

30J

Energy Conservation With Conservative Forces: A bead is moving with a speed of 20 m/s at position A on the track shown in the figure. This track is friction-free, and there is no appreciable air resistance. What is the speed of the bead at point C?

34

Work-Energy Theorem: A 1000-kg car experiences a net force of 9500 N while slowing down from 30 m/s to 15.9 m/s. How far does it travel while slowing down?

34

Energy Conservation With Conservative Forces: What is the minimum energy needed to lift a 1.0-kg rocket to a height of 200 km and to give it a speed of 8.0 km/s at that height? (Neglect air resistance and the small decrease in g over that distance.) 34 kJ34 J34 MJ34 TJ34 GJ

34MJ

Work-Energy Theorem: The kinetic friction force that a horizontal surface exerts on a 60.0-kg object is 50.0 N. If the initial speed of the object is 25.0 m/s, what distance will it slide before coming to a stop?

375m

Work-Energy Theorem: On an alien planet, an object moving at 4.0 m/s on the horizontal ground comes to rest after traveling a distance of 10 m. If the coefficient of kinetic friction between the object and the surface is 0.20, what is the value of g on that planet? 8.0 m/s212 m/s26.0 m/s210 m/s24.0 m/s2

4

Energy Conservation With Nonconservative Forces: A 30-N stone is dropped from a height of 10 m and strikes the ground with a speed of 13 m/s. What average force of air friction acted on the stone as it fell? 2.9 N0.13 kN1.2 N4.1 N7.2 N

4.1

Energy Conservation With Conservative Forces: A small 1.4-N stone slides down a frictionless bowl, starting from rest at the rim. The bowl itself is a hemisphere of radius 75 cm. Just as the stone reaches the bottom of the bowl, how hard is the bowl pushing on it? 1.4 N5.6 N0.70 N2.8 N4.2 N

4.2

Power: A sand mover at a quarry lifts 2000 kg of sand per minute a vertical distance of 12 m. The sand is initially at rest and is discharged at the top of the sand mover with speed 5.0 m/s into a loading chute. What minimum power must be supplied to this machine? 3.9 kW4.3 kW6.7 kW1.1 kW520 W

4.3

Energy Conservation With Conservative Forces: In the figure, a ball hangs by a very light string. What is the minimum speed of the ball at the bottom of its swing (point B) in order for it to reach point A, which is 1.0 m above the bottom of the swing?

4.4

Work: A crane lifts a 425 kg steel beam vertically upward a distance of 95 m. How much work does the crane do on the beam if the beam accelerates upward at 1.8 m/s2? Neglect frictional forces.

4.7 × 10^5 J

Energy Conservation With Conservative Forces: A prankster drops a water balloon from the top of a building. If the balloon is traveling at 29.1 m/s when it strikes a window ledge that is 1.5 m above the ground, how tall is the building? Neglect air resistance

45

Work: A traveler pulls on a suitcase strap at an angle 36° above the horizontal. If 555 J of work are done by the strap while moving the suitcase a horizontal distance of 15 m, what is the tension in the strap? 52 N56 N46 N37 N

46n

Work-Energy Theorem: A stone is moving on a rough level surface. It has 24 J of kinetic energy, and the friction force on it is a constant 0.50 N. What is the maximum distance it can slide? 2.0 m24 m48 m12 m

48m

Springs: A 10-kg mass, hung by an ideal spring, causes the spring to stretch 2.0 cm. What is the spring constant (force constant) for this spring? 49 N/cm0.20 N/cm20 N/m5.0 N/cm0.0020 N/cm

49

Energy Conservation With Conservative Forces: When you drop a pebble from height HH, it reaches the ground with speed VV if there is no air resistance. From what height should you drop it so it will reach the ground with twice speed?

4h

Gravitational Potential Energy: A stone is held at a height h above the ground. A second stone with four times the mass of the first one is held at the same height. The gravitational potential energy of the second stone compared to that of the first stone is

4x as much

Springs: If 4.0 J of work are performed in stretching an ideal spring with a spring constant (force constant) of 2500 N/m, by what distance is the spring stretched? 5.7 cm3.2 m0.3 cm5.7 m3.2 cm

5.7

Work-Energy Theorem: Which requires more work, increasing a car's speed from 0 mph to 30 mph or from 50 mph to 60 mph? 50 mph to 60 mph0 mph to 30 mphIt is the same in both cases.

50-60

Kinetic Energy: Which one has larger kinetic energy: a 500-kg object moving at 40 m/s or a 1000-kg object moving at 20 m/s? The 500-kg objectThe 1000-kg objectBoth have the same kinetic energy.

500kg obj

Kinetic Energy: A 1000-kg car is moving at 15 km/h. If a 2000-kg truck has 23 times the kinetic energy of the car, how fast is the truck moving? 72 km/h41 km/h51 km/h61 km/h

51

Work: Matthew pulls his little sister Sarah along the horizontal ground in a wagon. He exerts a force on the wagon of 60.0 N at an angle of 37.0° above the horizontal. If he pulls her a distance of 12.0 m, how much work does Matthew do? 433 J185 J720 J575 J

575

Energy Conservation With Conservative Forces: A spring-loaded dart gun is used to shoot a dart straight up into the air, and the dart reaches a maximum height of 24 meters. The same dart is shot up a second time from the same gun, but this time the spring is compressed only half as far (compared to the first shot). How far up does the dart go this time (neglect all friction and assume the spring is ideal)? 3.0 m6.0 m12 m48 m

6

Energy Conservation With Conservative Forces: A rock falls from a vertical cliff that is 4.0 m tall and experiences no significant air resistance as it falls. At what speed will its gravitational potential energy (relative to the base of the cliff) be equal to its kinetic energy?

6.3

Work-Energy Theorem: A sled having a certain initial speed on a horizontal surface comes to rest after traveling 10 m. If the coefficient of kinetic friction between the object and the surface is 0.20, what was the initial speed of the object? 6.3 m/s9.8 m/s7.2 m/s8.9 m/s3.6 m/s

6.3

Energy Conservation With Conservative Forces: If a spring-operated gun can shoot a pellet to a maximum height of 100 m on Earth, how high could the pellet rise if fired on the Moon, where g = 1.6 m/s2? 17 m100 m610 m160 m3.6 km

610

Power: At what minimum rate is a 60.0-kg boy using energy when, in 8.00 s, he runs up a flight of stairs that is 10.0-m high? 735 W75.0 W48.0 W4.80 kW

735

Springs: If the work done to stretch an ideal spring by 4.0 cm is 6.0 J, what is the spring constant (force constant) of this spring?

7500 N/m

Work: A child does 350 J of work while pulling a box from the ground up to his tree house at a steady speed with a light rope. The tree house is 4.0 m above the ground. What is the mass of the box?

8.9

Power: A 1500-kg car accelerates from rest to 25 m/s in 7.0 s. What is the average power delivered by the engine? (1 hp = 746 W) 90 hp60 hp70 hp80 hp

90

Springs: An ideal spring with a spring constant (force constant) of 22 N/m is stretched from equilibrium to 2.9 m. How much work is done in the process? 47 J93 J186 J121 J

93

Work: How much work would a child do while pulling a 12-kg wagon a distance of 4.3 m with a 22 N force? 95 J66 J52 J109 J

95J

Springs: A heavy dart and a light dart are launched horizontally on a frictionless table by identical ideal springs. Both springs were initially compressed by the same amount. Which of the following statements about these darts are correct? (There could be more than one correct choice.)

Both darts had the same initial elastic potential energy.

Gravitational Potential Energy: You and your friend, who weighs the same as you, want to go to the top of the Eiffel Tower. Your friend takes the elevator straight up. You decide to walk up the spiral stairway, taking longer to do so. Compare the gravitational potential energy of you and your friend, after you both reach the top.

Both of you have the same amount of gravitational potential energy at the top.

Work-Energy Theorem: Three cars (car L, car M, and car N) are moving with the same speed and slam on their brakes. The most massive car is car L, and the least massive is car N. If the tires of all three cars have identical coefficients of kinetic friction with the road surface, for which car is the amount of work done by friction in stopping it the greatest? The amount of work done by friction is the same for all cars.Car LCar MCar N

Car L

Work-Energy Theorem: You slam on the brakes of your car in a panic, and skid a certain distance on a straight level road. If you had been traveling twice as fast, what distance would the car have skidded, under the same conditions?

It would have skidded 4 times farther.

Kinetic Energy: A truck has four times the mass of a car and is moving with twice the speed of the car. If K t and K c refer to the kinetic energies of truck and car respectively, it is correct to say that

K t = 16K c.

Power: Two cyclists who weigh the same and have identical bicycles ride up the same mountain, both starting at the same time. Joe rides straight up the mountain, and Bob rides up the longer road that has a lower grade. Joe gets to the top before Bob. Ignoring friction and wind resistance, which one of the following statements is true?

The amount of work done by Joe is equal to the amount of work done by Bob, but the average power exerted by Joe is greater than that of Bob.

Work: You throw a baseball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of the work done by gravity while it goes down.

The work is negative on the way up and positive on the way down.

Energy Conservation With Conservative Forces: A lightweight object and a very heavy object are sliding with equal speeds along a level frictionless surface. They both slide up the same frictionless hill with no air resistance. Which object rises to a greater height?

They both slide to exactly the same height.

Energy Conservation With Conservative Forces: A heavy rock and a light rock are dropped from the same height and experience no significant air resistance as they fall. Which of the following statements about these rocks are correct? (There could be more than one correct cho

When they reach the ground, the heavier rock has more kinetic energy than the lighter rock.

Springs: The graphs shown show the magnitude F of the force exerted by a spring as a function of the distance x the spring has been stretched. For which one of the graphs does the spring obey Hooke's law

b

Work: Person X pushes twice as hard against a stationary brick wall as person Y. Which one of the following statements is correct?

both do zero work

Work-Energy Theorem: A 4.0 kg object is moving with speed 2.0 m/s. A 1.0 kg object is moving with speed 4.0 m/s. Both objects encounter the same constant braking force, and are brought to rest. Which object travels the greater distance before stopping? the 1.0 kg objectthe 4.0 kg objectBoth objects travel the same distance.It cannot be determined from the information given.

both obj travel the same speed

Energy Conservation With Nonconservative Forces: If a stone is dropped with an initial gravitational potential energy of 100 J but reaches the ground with a kinetic energy of only 75 J, this is a violation of the principle of conservation of energy. TrueFalse

f

Power: Jill does twice as much work as Jack does and in half the time. Jill's power output is

four times Jack's power output.

Energy Conservation With Conservative Forces: Joe and Bill throw identical balls vertically upward. Joe throws his ball with an initial speed twice as high as Bill. If there is no air resistance, the maximum height of Joe's ball will be eight times that of Bill's ball.two times that of Bill's ball.four times that of Bill's ball.roughly 1.4 times that of Bill's ball.equal to that of Bill's ball.

four times that of Bill's ball

Energy Conservation With Conservative Forces: A person stands on the edge of a cliff. She throws three identical rocks with the same speed. Rock X is thrown vertically upward, rock Y is thrown horizontally, and rock Z is thrown vertically downward. If the ground at the base of the cliff is level, which rock hits the ground with the greatest speed if there is no air resistance? Rock YRock ZRock XThey all hit the ground with the same speed.

hit ground at same speed

Work: Two men, Joel and Jerry, push against a car that has stalled, trying unsuccessfully to get it moving. Jerry stops after 10 min, while Joel is able to push for 5.0 min longer. Compare the work they do on the car. Joel does 25% more work than Jerry.Joel does 75% more work than Jerry.Jerry does 50% more work than Joel.Joel does 50% more work than Jerry.Neither of them does any work.

neither do any work

If the force on an object is in the negative direction, the work it does on the object must be

positive or negative

Power: If the units of your answer are kg ∙ m2/s3, which of the following types of quantities could your answer be? (There could be more than one correct choice.) Check all that apply.

power

Work-Energy Theorem: Three cars (car F, car G, and car H) are moving with the same speed and slam on their brakes. The most massive car is car F, and the least massive is car H. If the tires of all three cars have identical coefficients of kinetic friction with the road surface, which car travels the longest distance to skid to a stop?

same distance

Energy Conservation With Conservative Forces: A stone can slide down one of three different frictionless ramps, as shown in the figure. For which ramp will the speed of the ball be the greatest at the bottom?

same speed

Energy Conservation With Conservative Forces: Two frisky otters slide down frictionless hillsides of the same height but different slopes. The slope of the hill of otter 1 is 30°, while the slope of the hill of otter 2 is 60°. If both start from rest, which otter is moving faster when she reaches the bottom of her hill?

same speed at the bottom

Energy Conservation With Conservative Forces: Two objects, one of mass m and the other of mass 2m, are dropped from the top of a building. If there is no air resistance, when they hit the ground

the heavier one will have twice the kinetic energy of the lighter one.

Energy Conservation With Conservative Forces: A girl throws a stone from a bridge. Consider the following ways she might throw the stone. The speed of the stone as it leaves her hand is the same in each case.Case A: Thrown straight up.Case B: Thrown straight down.Case C: Thrown out at an angle of 45° above horizontal.Case D: Thrown straight out horizontally.In which case will the speed of the stone be greatest when it hits the water below if there is no significant air resistance?

the speed is the same

Energy Conservation With Conservative Forces: Swimmers at a water park have a choice of two frictionless water slides, as shown in the figure. Although both slides drop over the same height h, slide 1 is straight while slide 2 is curved, dropping quickly at first and then leveling out. How does the speed v1 of a swimmer reaching the bottom of slide 1 compare with v2, the speed of a swimmer reaching the end of slide 2?

v1 = v2

Energy Conservation With Conservative Forces: When you throw a pebble straight up with initial speed VV, it reaches a maximum height HH with no air resistance. At what speed should you throw it up vertically so it will go twice as high?

√2v