Work
What is the formula for work?
W = Fdcos(theta)
What is the formula for power and the unit?
Power = work/time, measured in Watts (W)
Name all 6 simple machines
lever, pulley, wheel & axle, inclined plane, screw, wedge
Name the two types of mechanical energy that we have discussed (Abbreviations are fine)
kinetic and potential (KE & PE)
A 10 kg box is at rest on a shelf that is 5 meters above the ground. How much total energy does it possess in this location.
490 J (all PE)
Mr. Bassetti pushes on a wall and it doesn't move. What kind of work is done. (+) (-) or 0?
0J of work (it never moves, d = 0)
TJ and Colin are a powerlifting contest. TJ can lift the weight above his head 10 times in 10 seconds while Colin does the same in 1 min. Who produces more power?
TJ since he does it faster. They both do the same amount of work.
What is the difference between ideal mechanical advantage (IMA) and actual mechanical advantage (AMA). [Do not just say one is ideal and one is not]
IMA only accounts for advantage on paper using the dimensions and doesn't account for friction and real world situations where AMA does.
What is the unit for energy?
Joules (J)
280 W
What type of force never* does work?
Does it take more power (effort) from your body to run UP the stairs or to run down the stairs? Why?
Running up the stairs because you are going against gravity.
What does a pulley do?
It changes the direction of the lifting force from up to down and can make things lighter depending on the number of pulleys.
When is KE = 0 and PE = 0?
KE = 0 when an object isn't moving.
PE = 0 when the object is on the ground.
It takes 60 J of work to push a box 6 meters across the floor. What force was needed to do this?
10 N
A ball is thrown up into the air and falls back down to the same spot. What kind of work is being down on the ball during its time in the air? (2 answers)
Negative work on the way up (slowing down) Positive work on the way down (speeding up)
A machine can complete a task using 100 W of power. If the same machine completes the same task in HALF the time, the amount of power needed is ...
200 W
Simple machines do two things: the first is to change the direction of the force, what is the second?
To reduce the amount of force needed to do the work.
Name a non-mechanical energy source.
chemical, thermal, radiant, acoustic (sound), electrical.
Provide an input arm and output arm of a lever that is 1 meter long that has a mechanical advantage of 3.
input arm = 0.75 m
output arm = 0.25 m
Provide an example of MOVING object where NO NET WORK is done.
Any object moving at a constant velocity.
What is the story behind why we use HORSEPOWER as a measurement for CAR ENGINES?
James Watt was trying to sell his steam engine. It was a marketing gimmick.
There are 3 classes of levers. Explain all 3. (i.e. where is the force and fulcrum?)
Class 1 - fulcrum in the middle, force produced on end.
Class 2 - fulcrum on the end, force produced in the middle.
Class 3 - fulcrum on one end, force produced on other end.
A car on the ground is moving with a KE of 35,000J and comes to a stop, bringing its KE down to 0J. Where did that energy go?
It changed forms to thermal energy. (Friction)
A 500 kg roller coaster starts from rest atop a 100 m high hill. How fast is the roller coaster going when it reaches the bottom of the hill?
PE = KE, so 500 x 9.8 x 100 = 490,000 J.
KE = 1/2mv2
490,000 = 1/2(500)v2
v2 = 1960 --> v = 44.27 m/s