Questions and Answers
What is the equation for work?
Work = Force × Distance
What is the unit for work?
joule (J)
What is the formula for power?
Power = Work / Time
What is the unit for power?
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A bar that is free to pivot about a fixed point is a ___________.
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An inclined plane reduces the force needed to move an object by [increasing/decreasing] the ________________ through which the force is applied.
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What is the equation for work?
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What is the unit for work?
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What is the formula for power?
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What is the unit for power?
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A bar that is free to pivot about a fixed point is a ___________.
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An inclined plane reduces the force needed to move an object by [increasing/decreasing] the ________________ through which the force is applied.
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What is the equation for work?
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What is the unit for work?
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What is the formula for power?
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What is the unit for power?
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A bar that is free to pivot about a fixed point is a ___________.
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An inclined plane reduces the force needed to move an object by [increasing/decreasing] the ________________.
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What is the formula for machine efficiency?
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Why will machine efficiency never be 100%?
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The amount by which a machine multiplies an effort force is called the ______________ advantage.
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What is the formula for mechanical advantage?
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The power of a machine measures what?
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Energy and work both are measured in units of ________________.
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Kinetic energy is energy due to ____________________.
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What is the formula for kinetic energy?
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What two factors determine an object's gravitational potential energy?
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Does increasing the velocity of an object increase its potential energy?
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Mechanical energy is the sum of ________________ energy and ______________ energy.
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At what point on a roller coaster is the gravitational potential energy the greatest?
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At what point on a roller coaster is the gravitational potential energy the lowest?
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In order for work to be done on an object, the movement and the force MUST be in the _________________ direction.
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If a box that is 70 kg is moved up 140 m, then how much work is done?
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If an 80 kg ball is moved across a floor for 80 m, then how much work is done?
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If 700 Joules of work is done in 70 seconds, then what is the power?
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If a 50 kg box is moved 10 m in 10 seconds, then what is the power?
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If two people do the same amount of work but one does the work faster than the other, do they have the same amount of power?
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Circle the simple machines and put a box around the complex machines.
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How can you reduce friction in a machine?
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What is the machine efficiency of a machine that has a work input of 150 Joules and a work output of 35 Joules?
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What is the machine efficiency of a machine that has a work input of 200 Joules and a work output of 50 Joules?
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A person puts 50 N of force into a lever. The lever lifts a 500 N box. What is the mechanical advantage of the lever?
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A person puts 25 N of force into a wheel and axle and moves a 200 N box. What is the mechanical advantage of the wheel and axle?
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What is the kinetic energy of an object with a mass of 80 kg and a velocity of 4.5 m/s?
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Study Notes
Work and Power
- Work can be calculated using the formula: Work = Force × Distance.
- The SI unit for work is the joule (J), equivalent to one Newton meter (N m).
- One joule equates to work done when a force of 1 N moves an object over 1 m.
- Power is computed with the formula: Power = Work / Time.
- The Watt is the standard unit of power, defined as 1 Joule/second.
Machines and Efficiency
- A fulcrum is a pivot point for a lever.
- Inclined planes and pulleys reduce the force needed by increasing the distance over which the force is applied.
- Machine efficiency is determined by the formula: Efficiency = (Output / Input) × 100%.
- Machine efficiency cannot reach 100% due to energy loss from friction.
Mechanical Advantage
- Mechanical advantage quantifies how much a machine multiplies an input (effort) force.
- It is defined as the ratio of load (resistance) to effort (applied force) and has no units.
- Simple machines include levers, pulleys, screws, and inclined planes, while bicycles and pulley systems (e.g., block and tackle) are complex machines.
Energy Concepts
- Kinetic energy (KE) is the energy of an object due to its motion, calculated with the formula: KE = 1/2 mv².
- Gravitational Potential Energy depends on mass, gravitational acceleration, and height.
- Mechanical energy is the sum of potential energy and kinetic energy in a system.
Work, Power, and Calculations
- Work requires force, movement, and both must be in the same direction.
- Work done moving a 70 kg box up 140 m is 98,000 J.
- Moving an 80 kg ball across a 80 m floor results in 6,400 J of work.
- If 700 Joules of work is done over 70 seconds, the power is 10 W.
Understanding Energy Transfer
- Gravitational potential energy is highest at the highest point of a roller coaster and lowest at the lowest point, where kinetic energy is highest.
- Increasing an object's speed does not change its potential energy but affects kinetic energy.
Mechanics and Friction
- To reduce friction in machines, consider using low-shear materials or rolling element bearings instead of sliding friction.
- Mechanical advantages calculated for levers and wheels provide insights into the effectiveness of these machines, e.g., a lever lifting 500 N with 50 N of input force yields a mechanical advantage of 10.
Efficiency in Machines
- Example efficiencies: a machine with 150 J input producing 35 J output has an efficiency of 4.2%; another with 200 J input and 50 J output achieves 4% efficiency.
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Description
Test your understanding of work, power, and the efficiency of machines with this quiz. Explore essential formulas and concepts that explain how machines make work easier. Perfect for students studying mechanics in physics classes.
