Unit Test/ October 2
Kristina demonstrates a toy for her younger brother. The steps to operate the toy are listed below. Step 1. Push the toy down. Step 2. A spring compresses. Step 3. Release the toy. Step 4. The toy jumps into the air. Which best describes Step 4?
Elastic potential energy changes to gravitational potential energy.
What best describes the energy in a closed system at the beginning of a day and the energy at the end of the same day? Check all that apply.
Some energy can be changed from one form to another. The total initial energy will be equal to the total final energy. Friction can cause the amount of thermal energy to increase.
A 535 kg roller coaster car began at rest at the top of a 93.0 m hill. Now it is at the top of the first loop-de-loop This roller coaster's track is nearly frictionless, so resistance can be ignored. Using g = 9.8 m/s2, what best describes the roller coaster car when it is at the top of the loop-de-loop?
The car has both potential and kinetic energy, and it is moving at 24.6 m/s.
Which statement about work and power correctly describes an automobile race?
The car that finishes last has the lowest power.
Efficiency is the ratio of output work to input work, expressed as a percentage. Light bulbs put out less light energy than the amount of electrical energy that is put into the bulb.
10%
The velocity of a 10.0 kg object that has 720 J of kinetic energy is
12 m/s
A 7.00 kg bowling ball is held 2.00 m above the ground. Using g = 9.80 m/s2, how much energy does the bowling ball have due to its position?
137 J
Natalia lifts a bag of groceries 0.50 m by exerting a force of 36 N. How much work did she do on the bag?
18 J
What is the potential energy of a spring that is compressed 0.65 m by a 25 kg block if the spring constant is 95 N/m?
20 J
What is the kinetic energy of a 620.0 kg roller coaster moving with a velocity of 9.00 m/s?
25,100 J
Tracy makes a list of energy transformations that occur as an engine runs to power a car. 1. Chemical energy transforms into thermal energy. 2. Thermal energy transforms into electrical energy. 3. Chemical energy transforms into gravitational potential energy. 4. Thermal energy transforms into kinetic energy. Which transformation should Tracy remove from the list?
3
A blender takes in 180 J of electrical energy. Of the 180 J, 90 J are transformed into kinetic energy, 60 J are transformed into thermal energy, and the rest is transformed into sound. What is the sound energy generated by the blender?
30 J
In which scenario is the least amount of work done on a crate?
A force of 130 N moves it 22 m.
A 440 kg roller coaster car is going 26 m/s when it reaches the lowest point on the track. If the car started from rest at the top of a hill, how much higher was that point on the track than the lowest point? (Use g = 9.80 m/s2, and ignore friction.)
34 m
A baseball has a mass of 0.145 kg and is 12 m above the ground. If it has a mechanical energy of 105.8 J, how fast is it moving?
35 m/s
A compressed spring has 16.2 J of elastic potential energy when it is compressed 0.30 m. What is the spring constant of the spring?
360 N/m
A famous motorcycle company has just built its first electric model. Like all vehicles, the purpose of the motorcycle is to put out kinetic energy.How much energy goes toward kinetic energy?
400 J
A diver who has a mass of 68 kg climbs to a diving platform that is 7.5 m above the surface of a pool. How much gravitational potential energy does the diver have in relation to the pool's surface?
4998 J
A 30.0 kg object has an initial velocity of 7.00 m/s and a final velocity of 10.0 m/s. The work done on the object is
765
The kinetic energy of an object with a mass of 6.8 kg and a velocity of 5.0 m/s is
85
In which scenario is an animal doing work? Check all that apply.
A cat lifts up her kitten by its neck. A bird carries a worm to its nest. A horse pulls a wagon along a road.
In which scenario is elastic potential energy present?
A fly stretches a spider web.
Irving, a cat, has a favorite toy that is made up of a squeaky ball at the end of a string. The toy makes up a closed system. Irving's owner dangles the toy so that the ball swings down and then swings back up again. Ignoring any friction, how are kinetic and potential energy related to each other as the ball swings back and forth?
As the ball moves upward, kinetic energy decreases and potential energy increases.
Which energy transformations occur when a candle burns?
Chemical energy transforms into thermal energy and radiant energy.
Which statement best describes what energy transfer diagrams show?
Energy can change form, but the total amount of energy stays the same.
Hiro walks up a flight of stairs in his apartment building. Later in the day, he runs up the same flight of stairs. Which statement about work and power describes Hiro's actions?
He had more power running than walking.
What is the unit for work?
Joule
Which equation represents the law of conservation of energy in a closed system?
KEi + PEi = KEf + PEf
Which best describes how energy changes form in a car's engine?
Multiple transformations occur because the chemical energy of the fuel is changed to several forms of energy.
Every spring has an equilibrium position. Which statements describe a spring at its equilibrium position? Check all that apply.
The elastic potential energy is zero. The net force acting on the spring is zero.
A load of bricks is lifted to the second floor of a building. How do work and power relate to this job?
The faster the job is done, the greater the power.
Rita throws a ball straight up into the air and catches it at the same position from which she threw it. The ball has 18 J of mechanical energy when it leaves her hand. If no energy is lost due to friction, which statements about the energy of the ball are true? Check all that apply.
The potential energy at the top of the ball's motion is 18 J. The kinetic energy increases as the potential energy decreases. The kinetic energy decreases as the potential energy increases. he total mechanical energy of the ball stays constant.
How do the units of work and power compare?
The unit for work is a joule. The unit for power is a watt, which is a joule per second.
How does the work needed to lift an object and the gravitational potential energy of the object compare?
They are equal.
Four vehicles are traveling on the same road. Which vehicle most likely has the greatest kinetic energy?
a pickup truck traveling at a velocity of 25 m/s
When energy is changed from one form to another, some of the energy is lost to the surroundings as waste thermal energy. The more steps needed to arrive at the desired energy or the more types of energy that are generated, the more energy is wasted. Which object would likely have the least amount of wasted energy?
a solar cell
Lester prepares to lift a heavy sack of flour into a customer's shopping cart. During which part of the action does Lester do work?
as he lifts the sack to his chest from the floor
Which change would cause the largest increase in a mountain climber's gravitational potential energy?
carrying twice the weight and climbing twice as high
Kinetic energy and mass are proportional
directly
Doubling which quantity would cause the largest increase in a spring's elastic potential energy?
displacement
Energy can be changed from one form to another. Which terms can be used to describe these changes? Check all that apply.
energy conversion energy transformation
What is the sequence of energy transformations associated with a hydroelectric dam?
gravitational potential energy into kinetic energy into mechanical energy into electrical energy
Which factor affects gravitational potential energy but not elastic potential energy?
mass
The measure of a spring's resistance to being compressed or stretched is the
spring constant
In physics, a is a group of related objects that interact with each other and form a complex whole.
system
Which formula can be used to find velocity if kinetic energy and mass are known?
v = Square Root of StartFraction 2 times K E over m EndFraction.
How is power calculated?
work/time
