Work
How is work defined in physics?
The use of force to move an object
What is power?
A measure of the amount of work that can be done in a given amount of time
What is a machine?
Any device that makes work easier by changing a force
Which type of simple machine is represented by a hammer?
A lever
Why is the output work of a machine always less than the input work done on the machine?
The machine must use some of the work to overcome friction.
What is the equation of work?
Work = Force × Distance.
What is the SI unit for power?
The Watt (W)
What are the 3 ways that machines may change a force?
Which type of simple machine is represented by a ladder?
An Inclined Plane
What is the efficiency of a machine?
The percent of work put into a machine by the user (input work) that becomes work done by the machine (output work). It is a measure of how well a machine reduces friction.
What is the SI unit for work?
The Joule (J) or The Joule (J)
What is the equation for Power?
Power=Work/time or Joules/seconds
Can a machine increase both the force and the distance over which the force is applied? Why or why not?
No. if the work is the same, a greater force requires less distance while a greater distance requires less force.
Which type of simple machine is represented by a knife?
A wedge
What is the efficiency of a machine equation?
Efficiency=Output Work/Input Work x 100%
Cassie helps her mom put the 300 newton lawn mower in the back of her mom’s truck. They lift the mower up from the ground to the truck bed, which is 1.05 meters above the ground. How much work do Cassie and her mom do?
315 J (N x m)
How much power does a toaster have if it does 1,000 joules of work in 50 seconds?
20W
A broom is an example of a machine. Where are the input and output forces applied?
Input: the top handle; the bottom brush
Which type of simple machine is represented by a doorknob?
Wheel and Axle
If a machine requires an input of 5000 joules of work to put out 4500 joules of work, what is the machine’s efficiency?
4500/5000 x 100%= 90%
Lile climbs into the back of the truck to tie the lawn mower in place. If she does 525 joules of work raising herself to the truck bed at 1.05 meters, how much force did she apply?
500 N
How much work can be done in 40 seconds by a 800-watt microwave oven?
32000J
How many Watts are in 1 horsepower (hp)?
746W
David’s mom has a car with a 200-horsepower engine. How many watts of power is that?
149,200W