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PHYSICAL SCIENCE EB CHAPTER 6
Terms in this set (35)
The product of the force and the distance
through which the force moves W=Fd
The time rate of doing work: power = work time
The unit of power , the joule per second
The property of a system that enables it to do work
The stored energy that a body possesses because of its position
Energy of motion, described by the relationship: Kinetic energy= mv2
The work done on an object is equal to the energy gained by the object: Work= triangleKE
Energy cannot be created or destroyed; it may be transferred from one form into another, but the total amount of energy never changes. In an ideal machine, where no energy is transferred into heat, work input= work output and (Fd)inout = (Fd)output
Conservation of Energy
A device such as a lever or pulley that increases (or decreases) a force or simply changes the direction of a force
The percent of the work put into a machine that is covered into useful work output
A force sets an object in motion. When the force is multiplied by the time of its application, we call the quantity impulse, which changes the momentum of that object. What do we call quantity force x distance?
Cite an example where a force is exerted on an object without doing work on the object.
A force is needed to hold a barbell overhead, but this force does no work on the barbell while the barbell is at rest.
Which requires more work- lifting a 50 kg sack a vertical distance of 2m or lifting a 25 kG sack a vertical distance of 4m?
Both require the same work because the force x the distance is the same for each.
If both sacks in the preceding question are lifted their respective distances in the same time, how does the power required for each compare? How about the same case where the lighter sack is moved its distance in half the time?
Power for each if the same because the work is done in the same time. Twice the power is required to do the same work on the lighter sack in half the time.
What are the two main forms of mechanical energy?
Potential Energy and Kinetic Energy
Exactly what is it that a body having energy is capable of doing?
A car is lifted a certain distance in a service station and therefore has a potential energy relative to the floor. If it were lifted twice as high, how much potential energy would it have?
Twice as much more
Two cars are lifted to the same elevation in a service station.If one car is twice as massive as the other, how do their potential energies compare?
The twice as massive car has twice the potential energy
How many joules of potential energy does a 1- N book gain when it is elevated 4 m?
potential energy= 1N x 4m= 4J. At 8m the potential energy= 8J
A moving car has kinetic energy. If it speeds up until it is going four times as fast, how much kinetic energy does it have in comparison?
As four times a fast car has 4 2squared or 16 times the KE
Compared to some original speed, how much work must the brakes of a car supply to stop a car moving four times as fast? How will the stopping distance compare?
A four times as fast car has 16 times as much KE and will require 16 times as much work to stop, and 16 times as much stopping distance.
What will the kinetic energy of pile driver ram when it undergoes a 10kJ decrease in potential energy? (Assume no energy goes to heat)
Can a machine multiply input force? Input distance? Input energy? ( If your three answers are the same, seek help, for the last question is especially important.)
YES; YES; NO (Machines are good at multiplying force or distance, but no machine can multiply energy- a conservation of energy no-no!)
If a machine multiplies force by a factor of four, what other quantity is diminished, and how much?
Increasing force means decreasing distance, so the distance moved by the four- fold force is one-fourth as much.
If the man in figure 6.21 pills 1 m of the rope downward with a force of 100N, and the load rises 1/7 as high, what is the maximum load that can be lifted?
Seven times as much, 700N
What is the efficiency of a machine that miraculously convert all the inout energy to useful output energy?
100%- The efficiency of an ideal machine
Is a machine physically possible that has an efficiency greater that 100%?
NO, not in the world as we know it. Such a machine would clearly violate the conservation of energy, a law that has never been violated.
What is the ultimate source of energies of fossil fuels, dams, and windmills?
What is the source of geothermal energy?
Nuclear energy from radioactive decay or steam energy from hot springs.
The energy we require for existence comes from the chemically stored potential energy in food, which is transformed into other forms when it is metabolized. What happens to a person whose work output is less than the energy he or she consumes? Whose work output is greater than the energy he or she consumes? Can an undernourished person perform extra work without extra food? Briefly explain.
When work output is less than input energy, the person gains weight. An undernourished person performing extra work without extra food violates energy conservation and would die or perish.
MA --> NEWTONS
FORCE x DISTANCE --> JOULES
MGH -- (MG= WEIGHT) (H= HEIGHT)
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