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Work and power
Terms in this set (55)
what is work?
occurs when a force causes an object to move in the direction of the force or w=Fd
what two conditions need to exist in order to do work?
1. object moves as force is applied
2. the direction of the object's motion is the same as the direction of the force applied
What is power?
the rate at which work is done or P=w/t
equation for work
what does work depend on?
what does power depend on?
unit for work
Joule (J) or Newton meter(N*m)
how are force and direction of motion related when talking about work?
If an object is pushed on, but does not move, is there any work being done on the object? Why?
NO, in order to do work, the force must push or pull on the object AND the object must move a distance in the direction of the force. Both need to happen to do work.
1.If a pencil drops from a desk, is work being done. Why?
2. If you answered yes, what is doing work on the pencil?
1. yes, a force and distance in the direction of the force is applied to the pencil
what would the triangle for work look like?
work on top
F and d on the bottom
When is more work being done: when lifting books from waist to shoulder height or when lifting the books from waist to over your head? Explain
over head, it is a greater distance to lift so the work would be increased w=Fd
Are you using more force when lifting two books or one?
2, more force is needed since they are heavier
A person pushes a block 4m with a force of 24N. How much work was done?
A person does 15J of work moving a couch 1.3m. How much force was used?
Paul Konerko hit a 125m grand slam in Game 2 of the World Series. He did 3000J of work. With what force did he hit the ball?
You lift a box that weighs 50N to a height of 1.7m. How much work did you do on the box?
A 750N skydiver jumps put of an airplane that is flying at an altitude of 2800m. By the time the skydiver reaches the ground, how much work was done on her by gravity?
A bulldozer performs 75,000 J of work pushing dirt 18m. What is the force exerted?
Mr. Z holds 200kg above his head for 5 seconds. What is his work done on the weights?
If Ms. Oldham has a mass of 55 kilograms and climbs up stairs that are 30 meters tall then how much work was done?
If 100 J of work are done by lifting a box 1.5m, then how much mass was the box?
You hurry to your physics class after a yummy meal in the cafeteria. In your arms you carry books that include your highly valued EMP binder. All the together the food and the binder weigh 22 N. How much work is done on the books when you walk 80 m along the hall, go up stairs 12 m high, and then turn right for an additional 15 m to class?
If an object was pushed on but does not move, is there any power being done?
no, there was no work being done
unit for power
Joules/second (J/s) or watts (W)
equation for power
what does the triangle for power look like?
work on top
power and time on the bottom
Dante uses 14 J of work to lift a weight for 30 seconds. How much power did he use?
A machine produces 4000 Joules of work in 5 seconds. How much power did the machine produce?
Ms. Johnson can bench press 150 kg from 0.7m from the ground to 1.5 m above the ground.
a. How much weight (not mass) did Ms. Johnson lift?
b. How much power did she use if she lifts the weights for 10 seconds?
b. 117.72 J/s
If it took Ms. Oldham 37 seconds to lift a 400 N student up 15 m, how much power did she use?
Darth Vader unleashed the power of the dark side (1225 W) on the unsuspecting Jedi. If he did 727 J of work, how much time did it take?
While playing 17 straight hours of the Wii, Mr. Wallaby successfully raised his arm to scratch his head 187 times. If he raised his hand 1m and his arm has a mass of 2.3 kg, how much power was used?
Superman moves a car 2700 N on a track of 500m. If the car takes 32 seconds to move the entire distance, how much (super)power is exerted by superman?
Superman is unhappy with his previous time(32s) and power(42187.5 J/s), so he attempts to lift the same car(2700N). This time, it takes 18.1 seconds to move it 500m. How much did his power increase?
If a man slowly lifts a 20kg bucket from a well and does 6 kilojoules of work (1000 Joules = 1kilojoule), how deep is the well?
Hulky and Bulky are two workers being considered for a job at the UPS loading dock. Husky boats that he can lift a 100kg box 2.0 m vertically in 3.0 seconds. Bulky counters with his claim of lifting a 200kg box 5.0 m vertically in 20 seconds. Which worker has a greater power rating?
Bulky: P= 490.5 J/s
You and a friend run up stairs that are 30m high. Both of you reach the top in 12 s. You weigh 570N and your friends weighs 620N. Which of you has more power and why?
Why: she has more force/weight --> more work --> more power
You: P= 1425J/s
Your friend: P = 1550 J/s
When did you do the most work, when you climbed the stairs slowly or quickly.
The SAME amount is done for each scenario
What two things could be changed to change the amount of work done?
distance and force
When did you use the most power, when you climbed the stairs slowly or quickly.
If the amount of Work done stays the same, what must happen to change the amount of power used?
time is reduced
A deflated hot air balloon weighs a total of 8000N. Filled with hot air, the balloon rises to a height of 1000m. How much work us accomplished by the hot air?
A rope is thrown over a beam, and one end is tied to a 300N bundle of lumber. You pull the free end of the rope 2m with a force of 400N to lift the lumber off the ground. How much work have you done? (hint: draw FBD)
STUDY!!! A 150N boy rides a 60N bicycle a total of 200 m at a constant speed. The frictional force against the forward motion of the bicycle equals 35N. How much work does the boy do?
Work= 0 J
You must exert a force of 4.5 N on a book to slide it across a table. If you do 2.7J of work in the process, how far have you moved the book?
A child pulls a sled up a snow-covered hill. The child does 405 J of work on the sled. If the child walks 15m up the hill, how large of a force must the child exert?
How much work is done on a small car if 3150 N of force is exerted to move it 75.5 m to the side of the road?
A crate is being lifted into a truck. If it is moved with a 2470 N force and 3650 J of work is done, then how far is the crate being lifted?
If 16,700 J of work is done to shoot the human cannonball down a 3.05m barrel, then how much force is applied to the person to fire them out of the cannon?
An elephant pushes with 2000N on a load of trees. It then pushes these trees for 150m. How much work did the elephant do?
An 190,000 W engine can accelerate from rest to a top speed in 9 s. How much work did the engine do?
Another engine reaches its top speed from rest in 7.5 s. It is able to perform 250,000 J of work in that time. How much power does this engine have in that time?
If a runner exerts 350 J of work to make 125 W of power, then how long did it take the runner to do the work?
A crane lifts a load of steel that weighs 9.3 x 10^5 N a distance of 100 m. It takes 5 minutes to complete the task.
a. How much work is done by the crane?
b. How much power does the crane produce?
a. 9.3 x 10^7 J
b. 3.1 x 10^5 W
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