Chapter 6: Work and Energy Conceptual Questions
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?
As they reach the ground, the 1 kg ball will be moving faster than the 2 kg ball Both balls will reach the ground with same kinetic energy mgh = ke
A 4 kg object is moving with a speed of 2 m/s. a 1 kg object is moving with a speed 4 m/s. Both object encounter the same constant braking force and are brought to rest. Which object travels the greater distance before stopping.
Both objects travel the same distance
If a stone is dropped with an initial gpe of 100 J but reaches the ground with a ke of only 75 J, this is a violation of the principle of conservation of energy
False
Jill does twice as much work as Jack does and in half the time. Jill's power output is
Four time Jack's power output Power is change of energy over time w/t 2w/t = w/2t 2*2 = 4
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...
Four time that of Bill's ball. .5mv^2 = mgh .5m(2v)^2 = mg(2h)
A stone is held at height h above the ground. A second stone with 4x the mass of the first one is held at the same height. The GPE of the second stone compared to the first stone is....
Four times as much mgh = (4m)gh
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. 2^2 = 4
A truck has four times the mass of a moving car and is moving with twice the speed of the car. If Kt and Ke refer to the kinetic energies of the truck and car respectively, it is correct to say...
Kt= 16Kc (1/2)*4*2^2= 16
Two men, Joel and Jerry, push against a car that has stalled, trying unsuccessfully to get the car moving. Jerry stops after 10 minutes, while Joel is able to push for 5 minutes longer. Compare the work they do on the car.
Neither of them do any work
If the units of your answer are kgm2/s3, which of the following types of quantities could your answer be?
Power
When you throw a pebble straight up with initial speed V, it reaches a maximum height H with no air resistance. At what speed should throw it up vertically so it will go twice as high?
SQRT2*V because SQRT2^2 = 2
Which 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 object. Velocity is squared and is more influential on the magnitude of kinetic energy
Two cyclists who weight 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. Ignore 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.
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 as kinetic energy as the lighter one. Ug = KE
Hooke's Law
The law stating that the stress of a solid is directly proportional to the strain applied to it.
A stone can slide down one of four different frictionless ramps, as shown in the figure. For which ramp will the speed of the ball be the greatest at the bottom.
The speed of the ball will be the same for all ramps. mgh = ke
If the force on an object is in the negative direction, the work it does on an object must be ....
The work could be either positive or negative, it depends on what direction the object is moving in
You throw a baseball straight up. Compare the sign of the work done by gravity while the ball goes up with the sign of work done by gravity while it goes down.
The work is negative on the way up because the force applied is in the opposite direction of the direction of the object, the work is positive on the way down because the force applied is in the same direction that the ball moves.
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?
They all hit the ground at the same time
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 fiction in stopping is it the greatest?
car L, because 0.5*m*v2 = -F*d*cos(180). They are all traveling at the same speed, so the extra mass makes it so that if the kinetic friction wasn't equal, it would travel the farthest, so in order to have those be equal, F has to be greater because they need to be equal
An ornament of mass 40 g is attached to a vertical ideal spring with a force constant (k) of 20 N/m. The ornament is then lowered very slowly until the spring stops stretching. How much does the spring stretch?
.0196 m F = -kx F = mg 40 * 9.8 / 20
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?
0 J Delta X is zero, work only cares about the start and end points, not what it took to get there.
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 degree angle above the horizontal. Which of the following statements about these grasshoppers are correct?
1 - At their highest point, both have the same amount of mechanical energy 2 - At their highest point, grass hopper B is moving faster than grasshopper A 3- At their highest point, grasshopper A has more gravitational potential energy than grasshopper B mgh = ke but grasshopper A reaches a high h and therefor must be moving slower because energy must be conserved.
A heavy rock and a light rock are dropped from the same height and experience no air resistance. Which of the following statements about these rocks are correct
1 - Both rocks will have the same speed when they reach the ground 2 - When they reach the ground, the heavier rock has more kinetic energy than the lighter rock mgh = ke
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?
1 - Both sleds will slide the same distance on the rough snow before stopping 2 - The friction from the snow will do more negative work on the heavy sled than on the light sled
A heavy frog and a light frog jump straight into the air. They push off in such a way 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?
1 - Just as they leave the ground, the heavier frog will be moving faster than the lighter frog 2 - Both frogs reach the same maximum height
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
1 - The darts both have the same kinetic energy just as they move free of the spring 2 - The lighter dart leaves the spring moving faster than the heavy dart 3 - Both darts had the same initial elastic potential energy
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?
1 - The light dart goes higher than the heavier dart 2 - At the maximum height, both dart have the same GPE energy must be conserved
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 some 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?
1 - The light sled wills slide farther on the rough snow than the heavy sled 2 - On the rough snow, the change in kinetic energy will be the same for both sleds 3 - The friction from the snow will do the same amount of work on both sleds
A heavy stone and a light stone are released from rest in such a way that they both have the same gpe just as they are released. Which of the following statements about these stones are correct?
1 -The initial height of the light stone is greater than the initial height of the heavy stone 2 - Just as it reaches the ground, the light stone is traveling faster thn the heavy stone 3 - The stones both have the same kinetic energy as they reach the ground mgh = ke
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?
12P w/t = power 6/.5t = 12
When you drop a pebble from height H, it reaches the ground with kinetic energy K 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 mgh = .5mv^2 mgh = 2(.5mv^2) mg2h = 2(.5mv^2)
Person X pushes twice as hard against a stationary brick wall as person Y. What is true of the work done in this situation?
Both do zero work
You and your friend, who weights 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 GPE at the tope of the tower. mgh = mgh
When you drop a pebble from height H, it reaches the ground with speed V if there is no air resistance. From what height should you drop it so it will reach the ground with twice speed
4H mgh = .5mv^2 mgh = .5m(2v)^2 mg(4h) = .5m(2v)^2
Which requires more work, increasing a car's speeding from 0 mph to 30 mph or from 50 mph to 60 mph?
50 mph to 60 mph because 30 miles < 60 miles
Two frisky otters slide down frictionless hillsides of the same height but different slopes. The slope of the hill of otter 1 is 30 degrees, while the slope of the hill of otter 2 is 60 degrees. If both start from rest, which otter is moving faster when she reaches the bottom of her hill?
Both otters have the same speed at the bottom
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 Thrown straight up Thrown straight down Thrown out at an angle of 45 above the horizontal Thrown straight out horizontally
The speed will be the same in all cases
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?
They all travel the same distance in stopping. Their mass doesn't matter. When the coefficient of friction value is high, the stopping distance of the moving object will become less. On the other hand, if the coefficient of friction value is low, the stopping distance of the moving object will become high. So equal coefficients means equal distances.
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.
Swimmers at water 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 the slide 2?
v1 = v2 mgh = mgh
