Questions and Answers
What do we call the quantity force x distance, and what quantity can this change?
work, changes energy
How many times more work is required to lift the barbell three times as high?
triples
Does Earth's gravity do any work on a satellite revolving around the Earth in a circular orbit?
False
What force acts on an object sliding at constant speed on a frictionless surface?
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Which requires more work, carrying a 420 N knapsack up a 200 m hill or carrying a 210 N knapsack up a 400 m hill? Why?
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In what sense is the physics teacher correct when suggesting Grace do no work all day?
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Is Grace working now as she carries the paper boxes down a 15 m long hall?
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What person does more work when two people of the same mass climb up the same flight of stairs in different times?
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Is it possible to get more work done out of a machine than what you put in?
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How are the pedals of a bicycle a simple pendulum?
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How does the amount of work done on an automobile by its engine relate to the energy content of its gasoline?
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In what two ways can a machine alter an input force?
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Is it possible for a machine to multiply energy or work output?
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What is the efficiency of a machine that requires 100 J of input energy to do 35 J of useful work?
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What is the efficiency of a cyclist's body when expending 1000 watts of power to deliver mechanical energy to the bicycle at the rate of 100 W?
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Study Notes
Work and Energy
- Impulse is defined as force multiplied by the time of application, impacting an object's momentum.
- The quantity defined as force multiplied by distance is known as "work," which can change an object's energy.
Lifting and Height
- Lifting a barbell three times as high requires three times more work compared to lifting it once.
Forces and Orbits
- A satellite in a circular orbit experiences no work done by Earth's gravity since the force and displacement are at 90 degrees to each other.
Motion on a Frictionless Surface
- An object sliding at a constant speed on a frictionless surface experiences the force of gravity downward and the normal force upward, resulting in no work being done.
Comparing Work
- Carrying a 420 N knapsack up a 200 m hill and carrying a 210 N knapsack up a 400 m hill requires the same amount of work since work is dependent on weight and height lifted.
Work by Grace
- When Grace carries paper up and down stairs, positive work occurs when lifting the paper, while negative work occurs while descending, leading to a net work of 0 J for the entire day.
Work in Different Directions
- When carrying items down a level, if the force and displacement are at 90 degrees, no work is done, resulting in 0 J.
Power and Work Consistency
- Two people of the same mass climbing stairs exert the same amount of work; however, the person who climbs in 25 seconds exerts more power, as power is work done over time.
Machine Efficiency
- A machine cannot output more work than what is inputted; it may achieve ideal conditions (theoretical maximum work) or actual conditions (less output).
Pendulum and Bicycle Comparison
- The pedals of a bicycle operate similarly to a simple pendulum, utilizing the wheel and axle mechanism.
Energy and Engine Work
- The energy contained in gasoline is converted into work done by an automobile's engine, illustrating energy transformation.
Machine Input Force Alteration
- A machine can alter an input force by changing its size and/or direction, allowing for more versatile applications.
Law of Energy Conservation
- Machines abide by the law of energy conservation, permitting only the same amount or less of energy output compared to input.
Calculating Machine Efficiency
- A machine that requires 100 J of input energy and produces 35 J of useful work achieves an efficiency of 35%.
Human Efficiency
- A cyclist expending 1000 watts of power for only 100 W of mechanical energy results in a body efficiency of 10%, indicating substantial energy loss during the process.
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Description
Test your understanding of work and energy concepts, including impulse, lifting, and forces in different scenarios. This quiz will challenge your knowledge of how work is defined and calculated in physics, particularly in relation to gravitational force and motion. See how well you can apply these principles!
