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Questions and Answers
What is the IMA of a 120m long ski lift that carries skiers to a second station 40m above?
What is the IMA of a 120m long ski lift that carries skiers to a second station 40m above?
3
An inclined plane reduces the effort force by?
An inclined plane reduces the effort force by?
increasing the distance through which the force is applied
What is the ideal mechanical advantage of a pulley system equal to?
What is the ideal mechanical advantage of a pulley system equal to?
number of rope segments supporting the load
Why is the efficiency of a machine always less than 100 percent?
Why is the efficiency of a machine always less than 100 percent?
What is a wheel and axle?
What is a wheel and axle?
What is the SI unit of power?
What is the SI unit of power?
What is the AMA of a crowbar if you apply 40N of force to lift a 400N rock?
What is the AMA of a crowbar if you apply 40N of force to lift a 400N rock?
If you perform 40 joules of work lifting a 10N box, how high is the shelf?
If you perform 40 joules of work lifting a 10N box, how high is the shelf?
How is the IMA of a wheel and axle found?
How is the IMA of a wheel and axle found?
When is a machine classified as a compound machine?
When is a machine classified as a compound machine?
What can you calculate if you know the input distance and output distance of a machine?
What can you calculate if you know the input distance and output distance of a machine?
Compare the actual mechanical advantage to the ideal mechanical advantage.
Compare the actual mechanical advantage to the ideal mechanical advantage.
In which of the following is no work done?
In which of the following is no work done?
Give an example of a compound machine.
Give an example of a compound machine.
How much work do you do if you exert a force of 10N to lift a box a distance of 0.9m?
How much work do you do if you exert a force of 10N to lift a box a distance of 0.9m?
How can a machine make work easier for you?
How can a machine make work easier for you?
What is the efficiency of a device that requires 420J of work to do 230J of work?
What is the efficiency of a device that requires 420J of work to do 230J of work?
How much power do you use if you exert a force of 700N to walk 6m up a flight of stairs in 6 seconds?
How much power do you use if you exert a force of 700N to walk 6m up a flight of stairs in 6 seconds?
What is the unit of work?
What is the unit of work?
How many horsepower are 3730 watts?
How many horsepower are 3730 watts?
What does the power of a machine measure?
What does the power of a machine measure?
How can you make the work output of a machine greater than the work input?
How can you make the work output of a machine greater than the work input?
What might a 750W motor also be rated as?
What might a 750W motor also be rated as?
What kind of machine is an ax?
What kind of machine is an ax?
What happens when you reduce friction in a machine?
What happens when you reduce friction in a machine?
When does a force acting on an object do no work?
When does a force acting on an object do no work?
To increase power, you can decrease the amount of work you do in a given amount of time.
To increase power, you can decrease the amount of work you do in a given amount of time.
To increase power, you can increase the amount of work you do in a given amount of time.
To increase power, you can increase the amount of work you do in a given amount of time.
What amount of work must be supplied to a motor that has an efficiency of 75 percent to provide 240J of useful work?
What amount of work must be supplied to a motor that has an efficiency of 75 percent to provide 240J of useful work?
When a machine does work, what can it do to force?
When a machine does work, what can it do to force?
What can a machine multiply?
What can a machine multiply?
For work to be done on an object, what must happen to the object?
For work to be done on an object, what must happen to the object?
The bottle opener is what class of lever?
The bottle opener is what class of lever?
What does a machine change?
What does a machine change?
The fulcrum is always between the effort force and the resistance force in a what kind of lever?
The fulcrum is always between the effort force and the resistance force in a what kind of lever?
Any part of a force that does not act in the direction of an object's motion does no what on an object?
Any part of a force that does not act in the direction of an object's motion does no what on an object?
What do two or more simple machines working together make up?
What do two or more simple machines working together make up?
What is the force that is exerted on a machine called?
What is the force that is exerted on a machine called?
What is the mechanical advantage of a machine?
What is the mechanical advantage of a machine?
Which has the greater IMA?
Which has the greater IMA?
Why don't you do work as you hold a book motionless over your head?
Why don't you do work as you hold a book motionless over your head?
Why is the work output of a machine never equal to the work input?
Why is the work output of a machine never equal to the work input?
Which of these is NOT done by a machine?
Which of these is NOT done by a machine?
A car stereo does 300J of work in 6s. How much power do you use?
A car stereo does 300J of work in 6s. How much power do you use?
How much work is done if a dozen bagels weighing 11N are lifted a distance of 1.5m?
How much work is done if a dozen bagels weighing 11N are lifted a distance of 1.5m?
If a human brain generates 20 watts of energy in 35 seconds, how much work is done?
If a human brain generates 20 watts of energy in 35 seconds, how much work is done?
What is the IMA of a pulley that can lift a 1185N weight with 395 N of exerted force?
What is the IMA of a pulley that can lift a 1185N weight with 395 N of exerted force?
Find the force a person exerts in pulling a wagon 20m if 2000J of work is done.
Find the force a person exerts in pulling a wagon 20m if 2000J of work is done.
How could you increase the IMA of an inclined plane?
How could you increase the IMA of an inclined plane?
In which of the following situations do your arms do work on books?
In which of the following situations do your arms do work on books?
What is the IMA of a wheel and axle where the wheel has a radius of 10m and the axle has a radius of 2m?
What is the IMA of a wheel and axle where the wheel has a radius of 10m and the axle has a radius of 2m?
What type of simple machine is your foot when you stand on your toes?
What type of simple machine is your foot when you stand on your toes?
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Study Notes
Ideal Mechanical Advantage (IMA)
- A ski lift with a length of 120m and a height of 40m has an IMA of 3.
- The IMA of a wheel and axle is calculated by dividing the radius of the wheel by the radius of the axle.
- A pulley system's IMA equals the number of rope segments supporting the load.
- A screw with closely spaced threads has a greater IMA compared to one with threads spaced farther apart.
Machines and Work
- An inclined plane reduces effort by increasing the distance through which force is applied.
- A compound machine consists of two or more simple machines working together.
- No work is done if a force does not act in the direction of an object's motion, such as holding a book motionless.
- A machine can make work easier by changing the direction of force or multiplying the force.
Efficiency and Power
- Efficiency of a machine is calculated as (Output/Input) x 100%, with 100% efficiency being unachievable due to energy lost to friction.
- A motor rated at 750W can also be described as 1 horsepower.
- Power measures the rate of doing work, with the SI unit being the watt.
- To increase power, either the amount of work done or the time taken must be adjusted.
Work Calculation
- Work is calculated using the formula: Work = Force x Distance.
- Lifting a box with a force of 10N over a height of 0.9m requires 9 joules of work.
- A bag of bagels weighing 11N lifted 1.5m does 16.5J of work.
- The work output cannot equal the work input due to friction losses.
Real-Life Applications and Examples
- The actual mechanical advantage for a crowbar lifting a 400N rock with a 40N effort is 10.
- A bicycle and scissors serve as examples of compound machines.
- In everyday use, work done in lifting an object results in a change of position, thus confirming that work has been performed.
Levers and Forces
- The fulcrum is located between the effort and resistance forces in a first-class lever.
- The force applied to a machine is termed the input force.
- Each part of a force that does not align with an object’s motion does not contribute to work.
Miscellaneous Facts
- Energy generated by a human brain in 35 seconds equals 700J.
- If you need to lift a crate using a motor with an efficiency of 75%, it must supply 320J to achieve 240J of useful work.
- A second-class lever function is exemplified by standing on one's toes.
- In carrying books, work is done when lifting them from the floor, but not when holding them stationary.
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