Download Chapter 12 Test Study Guide: Simple Machines WORK A force

Chapter 12 Test Study Guide: Simple Machines
WORK
A force exerted on an object that causes it to move is called work.
*In order for work to be done, a force must be exerted over a certain distance. (The direction of the force and motion must be the
same for maximum work to be done.)
Ex: Opening a door to enter a room is an example of work being done on an object.
Work is measured in units called joules.
Much of the work done on rusty machines is lost due to friction.
POWER
The rate at which work is done is called power.
Power is measured in units called watts.
EFFICIENCY
An ideal machine would have an efficiency of 100 percent.
SIMPLE MACHINES
The wedge, screw, and lever are all examples of simple machines.
Pulleys change the direction over which a force is exerted.
A wedge is a simple machine that might be thought of as an inclined plane that moves.
A ramp is an example of a simple machine called an inclined plane.
A screw could be considered an inclined plane that wraps around a cylinder.
The fixed point that a lever pivots around is called the fulcrum.
Pulleys are often used to raise or lower a flag on a flagpole.
Fixed Pulley (A)-mechanical advantage of 1
Machine 5 above has the highest mechanical advantage; it’s the most complex
COMPOUND MACHINES
A machine that utilizes two or more simple machines is called a compound machine.
One example of a compound machine is a car.
Calculations
You will need to know how to use the formulas to solve problems.
*Work =Force x Distance
*Mechanical Advantage = Output force ÷ Input force
*Power =Work ÷ Time
*Efficiency= (Output work ÷ Input work) x 100
*Mechanical advantage of inclined plane=length of inclined plane ÷ distance of inclined plane
*Mechanical advantage of a compound machine=m. a. of machine 1 x m. a. of machine 2
SAMPLE QUESIONS
1.If you exert a force of 10 Newtons to push a desk 5 meters, how much work do you do on the desk? Show your work and include proper units.
Answer: 50J
2.Ramp #1 has a length of 2 meters. The height of ramp #1 is 1 meter. Ramp #2 has a length of 3 meters and a height of 2 meters. Calculate the
mechanical advantage of each ramp to determine which has the highest.
Mechanical advantage of ramp #1is 2
Mechanical advantage of ramp #2 is 1.5
3.You exert a 2N force on a doorknob. The doorknob exerts a 8N force on the screw. Calculate the mechanical advantage of the doorknob.
Answer:4
4.Taylor must apply 30J of work to ride her unicycle. The unicycle’s output work is 15J. What is the efficiency of the unicycle? Answer:50%
5.Machine #1 can do 3,000 joules of work in 10 seconds. Machine #2 can do 2,000 joules of work in 20 seconds. Calculate the power of the
following machines to answer the question that follows.
Power of machine #1: 300W
Power of machine #2: 100W
Which machine is more powerful? machine #1
6.The output force of a lever with an ideal mechanical advantage of 5 is used as the input force of a pulley system with an ideal mechanical
advantage of 2. What is the ideal mechanical advantage of the compound machine? Answer: 10