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87 Cards in this Set

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A machine moves a 500 N object 8 m. If the work input is 5700 J, what is the efficiency of the machine?
W(out) = F(out) x d(out)
= 500 N x 8 m
= 4000 J

efficiency = [ W(out) / W(in) ] x 100 %
= (4000 J / 5700 J) x 100 %

ANSWER: efficiency = 70 %
What is the mechanical advantage of a machine that increases distance?
MA < 1
A pulley system operates with a 60 % efficiency. It the work input is 175 J, how much useful work is produced? (Hint: Rearrange the formula for efficiency.)
W(out) = [efficiency x W(in)] / 100 %

=[ 75 % x 175 J ] / 100 %

= 131.25 J
What is a MACHINE?
A device that makes work easier.
4700 J of work is done on a machine that is 80 % efficient. What is the work output?
W(out) = [ efficiency x W(in)] / 100 %

= [ 80 % x 4700 J ] / 100 %

ANSWER: W(out) = 3760 J
What is another name for output force?
resistance force
Using a first-class lever, a person applies a 90 N force and moves the lever 3 m. This moves a 375 N rock at the other end .5 m. What is the efficiency of the lever?
W(in) = F(in) x d(in)
= 90 N x 3 m
= 270 J

W(out) = F(out) x d(out)
= 375 N x .5 m
= 225 J

efficiency = (work output / work input) x 100 %
= (225 J / 270 J) x 100 %
= 69 %
Name three ways a machine can make work easier.
Change the amount of FORCE that is exerted, the DISTANCE over which it acts, or the DIRECTION of a force.
A 200 N force applied to a machine lifts an 800 N object. What is the mechanical advantage of the machine?
Mechanical Advantage = Resistance Force / Effort Force

MA = F(R) / F(E)
= 800 N / 200 N

ANSWER: MA = 4
What is the mechanical advantage of a machine that increases force?
MA > 1
What type of lever is a seesaw?
first-class lever
What characteristic of an object is related to its mass and is often the resistance that a machine must overcome in doing work?
weight
What type of lever is a crowbar?
first-class lever
What is the mechanical advantage of a machine that changes only the direction over which a force acts?
MA = 1
What two simple machines make up a pair of scissors or pliers?
double first-class lever and a wedge (the blades)
What is the LAW OF CONSERVATION OF WORK as it relates to machines?
The total amount of work that is done on a machine is equal to the total amount of work that a machine does on an object.

W(in) = W(out)
If the effort force is closer to the fulcrum in a first-class lever, is its mechanical advantage greater than one, less than one, or equal to one? Explain.
MA , 1

The effort arm is smaller than the resistance arm. Therefore, the effort force is greater than than the resistance force. Force is decreased and distance increase so the mechanical advantage is less than one.
What is the DEFINITION of WORK INPUT?
Work input is the work that is done on a machine.
What type of lever is a baseball bat?
third-class lever
What FORMULA is used to calculate MECHANICAL ADVANTAGE of a machine when the forces are known?
Mechanical Advantage = Resistance Force / Effort Force
To increase force and have a mechanical advantage of greater than one, what must be closer to the fulcrum of a lever, the resistance force or effort force?
RESISTANCE FORCE (the effort force must be furthest from the fulcrum)
What is another name for input force?
effort force
To increase force and have a mechanical advantage of greater than one, what must be closer to the fulcrum of a lever, the resistance force or effort force?
RESISTANCE FORCE (

The effort force must be furthest from the fulcrum to increase mechanical advantage.)
What is the law of conservation of work modified for real systems?
W(in) = W(out) + friction
What type of lever is a hammer?
third-class lever
What are the SIX types of SIMPLE MACHINES?
1.) inclined plane
2.) wedge
3.) screw
4.) lever
5.) pulley
6.) wheel and axle
What type of lever is a broom or rake?
third-class lever
What is the UNIT of MECHANICAL ADVANTAGE?
It has no units. MA is just a number.
What type of lever is a wheelbarrow?
second-class lever
What is the DEFINITION of WORK OUTPUT?
Work output is the work that a machine does on an object.
Is the mechanical advantage of a second-class lever always greater than one, less than one, or equal to one? Explain.
MA > 1

By definition, the effort force is located further from the effort force in a second-class lever. Therefore, the effort arm is longer than the resistance arm and the effort force is smaller than the resistance force. Since force is multiplied, the mechanical advantage is greater than one.
What is the FORMULA for WORK OUTPUT?
WORK OUTPUT = RESISTANCE FORCE X DISTANCE (over which the resistance force acts)

OR

W(out) = F(out) x d(out)
What type of lever is a door?
second-class lever
What two simple machines are a special case of an inclined plane?
wedge and screw
What type of lever is a fishing pole?
third-class lever
Can the efficiency of a real machine ever be 100%? Why or why not?
No, it can not be because some work that goes into the machine is used to overcome friction which reduces the efficiency.
If the resistance is closer to the fulcrum than the effort force in a first-class lever, is its mechanical advantage greater than one, less than one, or equal to one? Explain.
MA > 1

If the resistance is closer to the fulcrum, then the effort arm is longer than the resistance arm and the effort force is smaller than the resistance force. Therefore, force is multiplied and the mechanical advantage is greater than one.
A machine has a mechanical advantage of 3. If a 500 N force is applied to the machine, how much force will the machine produce?
Reaarange the equation for mechanical advantage for the resistance force.

F(R) = MA x F(E)
= 3 x 500 N

ANSWER: 1500 N

What kind of simple machine is used to pull down the shades over a window?
pulley (fixed)
Using measurable distances, what is the FORMULA used to calculate the MECHANICAL ADVANTAGE of a wheel and axle?
Mechanical Advantage = Radius of Wheel / Radius of Axle
Is the mechanical advantage of a third-class lever always greater than one, less than one, or equal to one? Explain.
MA < 1

By definition, the resistance force is located furthest from the fulcrum in a third-class lever. Therefore, the resistance arm is greater than the effort arm and the resistance force is smaller than the effort force. Force is decreased and distance is increased, resulting in a mechanical advantage of less than one.
What is the FORMULA for EFFICIENCY?
efficiency = (work output / work inpout)x 100%
How do you CALCULATE the MECHANICAL ADVANTAGE of a PULLEY?
Count the number of sections of rope that support an object.
What type of simple machine is an ax or a knife?
wedge
A machine used to lift a crate of apples has an efficiency of 65 %. If a crate of apples weighing 1500 N is lifted 35 m, how much work must be put into the machine?
W(out) = F(out) x d(out)
= 1500 N x 35 m
= 52,500 J

W(in) = [ W(out) x 100% ] / efficiency
= (52,000 J x 100 %) / 65 %

ANSWER: W(in) = 80,769 J
What is the only class of lever that can have a mechanical advantage of greater than one, less than one, or equal to one?
first-class lever
What is the FORMULA for WORK INPUT?
W(in)= F(in) x d(in)

OR

WORK INPUT = EFFORT FORCE X DISTANCE (over which the effort force acts)

What type of simple machine is a zipper?
wedge
What UNITS is EFFICIENCY always expressed in?
It is always expressed as a PERCENT (%).
What type of machine is a merry-go-round?
wheel and axle
How is the DEFINITION of MECHANICAL ADVANTAGE?
The mechanical advantage of a machine is how many times it multiplies the effort force.
What type of lever is a bottle-opener?
second-class lever
What is the efficiency of an ideal machine?
100 %
What is a FULCRUM?
The point of rotation at which a lever pivots or turns about.
A man expends 150 J of work to move a box up an inclined plane. The amount of work produced is 125 J. What is the efficiency of the machine?
efficiency = (work output / input) x 100 %

efficiency = (125 J/ 150 J) x 100 %

ANSWER: efficiency = 83 %
Which type of pulley would you use to raise a flagpole? Explain.
fixed pulley

It raises the object and makes work easier by changing the direction of the force. A mechanical advantage of one is sufficient for the mass of a flagpole.
A person in a wheelchair exerts a force of 40 N to go up a ramp that is 8 m long. The weight of the person and the wheelchair is 60 N and the height of the ramp is 4 m. What is the efficiency of the ramp?
W(in) = F(in) x d(in)
= 40 N x 8 m
= 320 J

W(out) = F(out) x d(out)
= 60 N x 4 m
= 240 J

efficiency = (work output / work input) x 100%
= (240 J / 320 J) x 100%
= 75 %
What type of machine is the lid on a jar?
screw?
What two simple machines make up a screwdriver?
wedge and a wheel and axle
The neck acts as what type of lever in the body?
first-class lever
What three types of simple machines always have a mechanical advantage of greater than one?
inclined plane, wedge, and screw
What type of simple machine is a ramp?
inclined plane
Is the mechanical advantage of the wheel and axle of a screwdriver greater than, less than, or equal to one? Explain.
MA > 1 because the effort force is exerted on the wheel which acts over a larger distance than the axle. The resistance force is greater than the effort and mechanical advantage is increased.
Using the dimensions of an INCLINED PLANE, what is the FORMULA used to calculate its MECHANICAL ADVANTAGE?
Mechanical Advantage = Length of Incline / Height of Incline
Why is the mechanical advantage of an inclined plane, wedge, or screw always greater than one?
... because they always increase force.
What is the FORMULA used to calculate the mechanical advantage of a lever when the distances between the effort force, resistance force, and fulcrum are known?
Mechanical Advantage = Effort Arm / Resistance Arm
Is the mechanical advantage of the wheel and axle system of a bicycle greater than, less than, or equal to one? Explain.
MA < 1 because the effort force is applied to the axle which travels a smaller distance than the wheel each revolution. Therefore, distance is increased and force is decreased.
What type of pulley would you use to lift heavy construction materials to the top of a building? Explain.
PULLEY SYSTEM

Pulley systems have an increased mechanical advantage over fixed or moveable pulleys.
What is a WHEEL and AXLE?
A larger circular object (wheel) that turns about a smaller circular object (axle).
What type of pulley must be used to increase the mechanical advantage to greater than two? Explain.
PULLEY SYSTEM

A combination of fixed and moveable pulleys must be used to have three or more sections of rope support an object.
What is the ideal mechanical advantage of a fixed pulley always equal to? Explain.
MA = 1

Only one section of rope supports the object but the angle at which it is pulled changes the direction of the force.
How does a fixed pulley make work easier?
It changes the direction of a force.
Cars, watches, and dishwashers are examples of what type of machines?
compound machine
Why is the mechanical advantage of a machine always less than its ideal mechanical advantage?
Some work is always lost to friction.
What is the ideal mechanical advantage of a moveable pulley equal to? Explain.
IMA = 2

Two sections of rope support the object.
What is an INCLINED PLANE?
A flat, slanted surface.
The elbow and forearm act as what type of lever in the body?
third-class lever
What type of machine is a doorknob?
wheel and axle
What is a WEDGE?
An inclined plane that moves to raise an object along it or cuts or splits an object.
What is a LEVER?
A rigid bar that is free to move or pivot about a fixed point called a fulcrum.
What is a PULLEY?
A rope, belt, or chain wrapped around a grooved wheel.
How many classes of levers are there?
three
What type of lever is a nutcracker?
second-class lever
What is a SCREW?
An inclined plane wrapped around a cylinder.
What is a COMPOUND MACHINE?
A combination of two or more simple machines.
Your foot acts as what type of lever in the body?
second-class lever
What two types of pulleys make up a PULLEY SYSTEM?
fixed pulley and a moveable pulley