Ch 9
Review
Work, Power , Simple machines and Energy
Name______________________
What is the definition of:
1. Work- fxd; the amount of force it takes to move
an object.
2. Power- w/t the amount of work done in a period
of time
3. Joule- unit of work
4. Newton -unit of force
5. Watt-unit of power
6. Kilogram- unit of mass
7. Machine- a device that makes work feel easier;
does not change the amount of work
8. Lever- like a seesaw. Redirects force. Contains
fulcrum, effort, and resistance
9. Pulley- wheel with attached string; redirects
force
10. wheel and axle- axle is fixed, wheel turns, like a
fan
11. Inclined plane- slanted diagonal plane.
Increases distance and decreases force; like
stairs
12. Wedge- 2 inclined planes back to back; splits
things; like knife, zipper
13. Screw- inclined plane wrapped around a
cylinder
14. Compound machine- made of 2 or more simple
machines
15. Fulcrum, effort, resistance- parts of a lever
Questions:
1. What type of relationship exists between work and force?_direct__
2. What type of relationship exists between power and time?_inverse____
3. What is an example of a pulley? _flag pole___
4. A powerful person does work _quickly___while a weak person does work _slowly_.
5. Power is how quickly or slowly one can do work__.
6. Machines do the same amount of work but make doing work _feel easier___.
7. What can they change if they don’t change work (2 things)? Direction or amt of force; distance
8. What is an example of an inclined plane? stairs
9. What is an example of a wedge? Knife, ax What is it used to do? Split things
10. What is an example of a lever? seesaw
11. What is an inclined plane around a cylinder called? screw
12. What machines redirect the force? Pulley, lever
Solve the following problems – Use the proper format (picture, equation, substitution with units, and answer with units)
1. The brakes on a bicycle apply 200 N of frictional force to the wheels as the bicycle travels 10.0 m. How much
work did the brakes do on the bicycle.
w-fxd
w= 200 x10
w= 2000J
2. A mechanic uses a hydraulic lift to raise a 100 kg car 2 m off the ground. How much work does the lift do on the
car? (HINT – the force is equal to the weight of the car w=mg)
W=fxd
F=mg
F= 100 (9.8)
F= 980 N
W= 980 (2)
W= 1960 J
3. While rowing in a race, John does 6000 J of work on the oars in 60.0 s. What is his power output in watts?
P =w/t
P= 6000/60
P= 100 watts
4. Using a jack, a mechanic uses a force of 25000 N to lift a car 0.50 m in 50.0 s. What is the mechanic’s power
output?
P= w/t
P = fxd/t
P= 25000x.5 /50
P= 250 watts