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CONCEPTUAL PHYSICS
Work Power and Energy
___________________________________________________________
LESSON OBJECTIVES
Students will be able to...
 use appropriate metric units for given measurements
 describe the features of potential energy
 describe the features of kinetic energy
 define work
 understand the difference between conservative and non-conservative forces
 describe the Law of Conservation of Energy
 describe how friction causes energy loss
 describe power as energy expended per unit time
 list the six simple machines
 describe role of work, mechanical advantage and efficiency in the use of simple
machines
SKILLS
Students will be able to...
 use steps for solving physics problems
 solve problems using work, force, and distance
 solve problems using kinetic, potential energy, and the Law of Conservation of
Energy
 use bar diagrams as an aid for solving energy problems
 conduct experiments relating to work and energy.
 collect and display experiment data
Vocabulary
Work
power
energy
Gravitational potential energy
conservation of energy
elastic potential energy
kinetic energy
mechanical energy
compound machines
simple machines
potential energy
mechanical advantage efficiency
WORK- W=Fd, F=w/d, d=w/f,
CONCEPTS:
1.
_______________ is the unit for work.
2.
For work to be done, _______________ must be exerted through a distance.
3.
The formula for work is ______________________.
4.
1 Joule = _______________________
5.
__________________ is the ability to do work.
PROBLEMS
1.
How much work is done if you raise a 9.3 N weight 1.6 m off the floor?
2.
If a barbell weighs 120 N and you raise it 2.3 m, how much work is done?
3.
A force of 115.5 N is applied to move a cabinet 8.6m. How much work is done?
4.
How much work is done when a force of 66 N is used to lift a boulder 23 m.
5.
A force of 120 N was needed to lift a rock. A total of 220 J of work was done. How far
was the rock lifted?
6.
How high can a 50 N force move a load when 320 J of work is done?
*7. How much work is required to lift a 350 kg block 15 meters?
*8. Airflow lifts a 2.4 kg bird 63 m up. How much work was done by the flow.
*9. A forklift moves a 412 kg load 47 m. How much work was done by the forklift?
10. A crane lifts a container with a mass of 80 kg is lifted to a height of 9.6 meters. How much
work is done by the crane?
11.
A car engine applies a force of 65 N, how much work is done by the engine as it pushed a
car a distance of 75 m?
12.
A force does 30000 J of work along a distance of 9.5 m. Find the applied force.
13.
How high can a 40 N force move a load, when 395 J of work is done?
14.
How much work is required to lift a 500 kg block12 m?
15.
A 60 N force is applied over distance of 15 m. How much work was done?
16.
A railroad car is pulled through the distance of 960 m by a train that did 578 J of work
during this pull. How much force did the train supply?
17.
A boy pulls a sled at a constant speed 0.6 m/s by applying a force of 350 N. How much
work will be done during 1800 s?
18.
A light plane travels a distance of 150 m along a runway before takeoff. Find the work
done by the plane engine if it is applying a force of 13500 N.
19.
A horse pulls a carriage by applying 450 N of force. Find the traveled distance if the
horse did 89 J of work.k
20.
A truck travels at a constant speed of 45 m/s. How much work did the truck engine do
during a 2 hour period if it supplied a force of 25 N of force.k
21.
Airflow lifts a 3.6 kg bird 50 m up. How much work was done by the flow?
22.
Beatrice pushing is on a heavy box. Beatrice pushes with a force of 40 N. What
information do you need to determine if Beatrice is doing work on the box?
23.
Beatrice pushes the box 2 m to the right. What formula should you use to calculate the
amount of work done on the box?
24.
How much work does Beatrice do pushing the box?
25.
Write a definition for each of the following terms:
a. work
b. joule
26.
Calculate the amount of work done when a grocery store stocker uses 120 N of force to
lift a sack of flour 1.5 m onto a shelf.
27.
How much work is done on an object that is pushed .95 m with a force of 80 N?
28.
If 67 J of work is done to move a person, what force was used to push that person if he
was moved 19 m?
29.
A crate is moved 25 m across a warehouse by a group of three men. The push the crate
and do 500 J of work. What is the total force that was applied to the crate?
30.
Mary pulls her book bag off the floor and places it on top of her refrigerator. If the fridge
is 2.50 m high, what force did she use if she did 175 J of work?
31.
box?
You do 425 J of work to push a box 2.5 m up a ramp. What force did you apply to the
Power- P=W/T, W=PT, T=W/P, P=FV, F=P/V, V=P/F, V=D/T, F=PT/d,
M=PT/dg
79-91
1.. A heat engine does 23 J of work during 1800 s. Find the power supplied by the engine.
2. How much work is done by 15 W engine during 3.5 h?
3. How long must a 400 W electrical engine work in order to produce 300 J of work?
4. How much power is required when using a 12 N force to push an object at a velocity of 3 m/s?
5. An elevator motor in a high-rise building can do 3500 J of work in 5 min. Find the power
developed by the motor.k
6. It takes 500 W of power to move an object 96 m in 12 s. What force is being applied to the
object?
7. A heat turbine can generate a maximum power of 250 W. How much work can the turbine do
in 7.8 h?m
8. How much time is required for a car engine to do 278 J of work, if its maximum power is 95
W?k
9. How much time is required for a elevator to lift a 2000 kg load up 28 m from the ground level,
if the motor can produce 13 W of power?k
10. A 50 W pump is used to pump up water from a mine that is 50 m deep. Find the mass of
water that can be lifted by the pump in 1.4 h.k
11. Some scientists calculated that a whale can develop 150 W of power when it is swimming
under the water surface at a constant speed 28 km/h. Find the resistance force of the water
exerted on the whale.k
12. A toy tractor travels at constant speed of 21.6 m/s. Find the power supplied by the engine if it
can supply a maximum force of 467 N.k
13.. A 7.35 W lathe can move an iron block at a constant speed by applying a force of 5.56 N.
Find the speed of the block.k
pk
14.
Ignacio is trying to move a rock uphill. What are the two equations you can use to
calculate the power Ignacio must use to move the rock?
15.
If the rock does not move, does Ignacio perform any work? Does he use any power?
16.
Besides the distance and the force being applied, what else do you need to know to find
the power Ignacio uses when he moves the rock?
17.
Ignacio does 50J of work on the rock and it takes him 10 s. How much power, in watts,
does he use?
18.
Carolina does the same amount of work on the rock but moves the rock in 5 s. How
much power, in watts, does she use?
19.
Calculate the average power, in watts, required to pull a car up a ramp if the amount of
work is 250 J over a period of 45 s.k
20.
What amount of power, is used when 1,500 J of work is done in 2 s.
21.
Determine the work done using 1.5 x 103 W of power in 2 minutes.
22.
A machine uses 1,300 W of power. If the machine runs for 30 seconds, what is the work
done by the machine?
23.
What amount of power is used to push a 50 N box up a 500m ramp in 60 seconds.
24.
Calculate the time, in seconds, needed to do 39 J of work if the power output is 18W.
25.
What time is needed to lift a rock doing 75 J of work and 100 W of power?
Gravitational Potential Energy (GPE):
1.
A 2.4 kg toy falls from 2 m to 1 m. What is the change in GPE?
2.
If (on earth) an object falls 18 m and loses 36 J of GPE. What is the object’s mass?
3.
A 1 Kg object loses 20 J of GPE as it falls. How far does it fall?
4.
A small, 3 kg weight is moved from 5 m from the ground to 8 m. What is the change in
potential energy?
5.
A man rides up in an elevator 12 m. He gains 6500 J of gravitational potential energy.
What is the man’s mass?
6.
When a 5 kg rock is dropped from a height of 6 m on Planet X, it loses 24 J of GPE.
What is the acceleration due to gravity on Planet X?
7.
What is the gravitational potential energy of a 450 Kg car at the top of a 25 m parking
garage?
8.
What is the change in gravitational potential energy of a 45 kg weight that is moved from
2 m to 18 m on earth? What is it on the moon (g = 1.6 m/s2)?
9.
A 0.25 kg book falls off a 2 m shelf on to a 0.5 m chair. What was the change in GPE?
10.
When a 0.5 kg rock is dropped from a height of 12 m on Planet Z, it loses 45 J of GPE.
What is the acceleration due to gravity on Planet Z?
Kinetic Energy (KE)
1.
How much kinetic energy does an 80 kg man have while running at 1.5 m/s?
2.
A bird flies at a speed of 2.3 m/s if it has 14 J of kinetic energy, what is its mass?
3.
A 6 kg object has a speed of 24 m/s. What is its kinetic energy?
4.
A rock hits the ground with a speed of 7 m/s and a kinetic energy of 100 J. What is the
rock’s mass?
5.
How much kinetic energy does a 4 Kg cat have while running at 9 m/s?
6.
What is the mass of an object moving with a speed of 4 m/s and a kinetic energy of 2000 J?
7.
A student runs to physics class with a speed of 6 m/s. If the student has 880 J of kinetic
energy, what is her mass?
ENERGY: Gravitational Potential Energy -Kinetic Energy
1.
A 1.2 kg ball is placed on top of a hill. The hill is 5 m high. What is the GPE?
2.
A .68 N bowling ball is placed a ramp 4.8 m high. What is the GPE?
3.
A .38 N cat will jump from a ledge that is 3.7 m high. What is the GPE?
4.
A 6.6 kg ball rolls downhill at 8m/s. What is the KE?
5.
A .58 kg dog runs down a hill at 4.2 m/s. What is the KE?
6.
A 600 N truck falls 52 m from a bridge. What is the GPE?
7.
A 158 kg roller coaster car will drop 97 m from the top of the ride. What is the GPE?
8.
The same roller coaster car drops at 8.4 m/s. What is the KE?
9.
A 140 kg boulder is dropped 6 m. What is the GPE?
10. A 39 N rock is dropped 18 m. What is the GPE?
Gravitational Potential Energy and Kinetic Energy Study Guide
1. Energy is _____________________________________________________.
2. The equation for work is : __________________________
3. Work is measured in _________________________.
4. The formula for calculating gravitational potential energy is
__________________________
Mass is measured in ____________________
Height is measured in __________________
Gravity = _____________________
5. What is the potential energy of a rock that has a mass of 14 kg that is sitting on top of a
hill 1412 m high?
6. A book sitting on a shelf 2.8 m high has a mass of .06 kg. What is the book’s potential
energy ?
7. A 1430 kg auto is parked on a steep slope 72 m high. What is the potential energy of
this auto?
8. What is the gravitational potential energy of a .045 kg booklet on top of a desk 2.6
meters high?
9. An automobile to be transported by ship has a mass of 1490 kg. If it is sitting on a lift 12
meters above the surface of the ship, what is the potential energy of the auto?
10. The equation for kinetic energy is:
___________________________________
11. What is the kinetic energy of a .05 kg ball traveling at a velocity of 3 m/s towards home
plate?
12. What is the kinetic energy of a bicycle with a mass of 10.6 kg traveling at a velocity of
2.6 m/s north?
13. A 3 kg bowling ball is rolling down the alley with a velocity of 6 m/s toward the pins.
What is the kinetic energy of the bowling ball?
14. A baseball is pitched with a speed of 40 m/s. If the baseball has a mass of 0.14 kg, what
is the kinetic energy?
15. What is kinetic energy of a 0.33 kg football thrown with a speed of 14 m/?
16. Gravitational Potential Energy is energy at __________________ or energy of
____________.
17. Kinetic is ______________________________________________________________
18. What is the Law of Conservation of Energy?
Elastic Potential Energy
1.
A spring with a spring constant of 120 N/m stretches by 0.02 m. What is the potential
energy of the spring?
2.
An elastic spring stores 45 J of potential energy when it is stretched by .02 m. What is the
spring constant?
3.
A 50 N force causes a spring to compress 0.09 m. The spring constant is 555.6 n/m.
What is the potential energy of the spring?
4.
An 80 N force causes a spring to compress 0.15 m. The spring constant is 533.33? What
is the potential energy of the spring?
5.
A spring with a spring constant of 200 N/m stretches by 0.03 m. What is the potential
energy of the spring?
6.
A spring stores 68 J of potential energy when it is stretched by .06 m. What is the spring
constant?
7.
How much elastic potential energy is stored in a spring with a spring constant of 150 N/m
when it is compressed .02 m?
8..
A spring stores 96 J of potential energy when it is stretched by .05 m. What is the spring
constant?
Conservation of Energy
psi60-78
1. A student uses a spring (with a spring constant of 180 N/m) to launch a marble vertically into
the air. The mass of the marble is 0.004 kg and the spring is compressed 0.03 m. How high will
the marble go?
2. A student uses a spring gun (with a spring constant of 120 N/m) to launch a marble vertically
into the air. The mass of the marble is 0.002 kg and the spring is compressed 0.04 m. How high
will the marble go?
3. A roller coaster has a velocity of 25 m/s at the bottom of the first hill. How high was the hill?
4. A projectile is fired vertically upward with an initial velocity of 190 m/s. Find the maximum
height of the projectile.