Download Energy/Power Web Pkt.

CP Physics
Name ____________________________________
Energy & Work
Use the following web site to answer these questions.
http://www.glenbrook.k12.il.us/gbssci/phys/Class/energy/ene
rgtoc.html
1.
In physics, work is defined as a _________ acting upon an object to __________
a ________________________________.
2.
Statement
Answer with Explanation
A teacher applies a force to a wall and
becomes exhausted.
A book falls off a table and free falls to
the ground.
A waiter carries a tray full of meals
above his head by one arm across the
room.
A rocket accelerates through space.
3.
Mathematically, work can be expressed by the following equation.
________________________________
(Note in Accelerated Physics we leave off the COS )
4.
The ___________ is the unit of work.
1 Joule = 1 Newton * 1 meter
1J = 1 N * m
Click on Calculating the Amount of Work Done by Forces
5.
Work Done in Diagram A Show Calculation:
Work Done in Diagram B Do Not Do:
Work Done in Diagram C Show Calculation:
6.
Free-Body
Diagram
A 10-N forces is applied to
push a block across a friction
free surface for a
Forces Doing Work
on the Object
Amount of Work Done
by Each Force
displacement of 5.0 m to the
right.
Free-Body
Forces Doing Work
on the Object
Amount of Work Done
by Each Force
Diagram
A 10-N frictional force slows
a moving block to a stop after
a displacement of 5.0 m to the
right.
A 10-N force is applied to
push a block across a
frictional surface at constant
speed for a displacement of
5.0 m to the right.
A 2-kg object is sliding at
constant speed across a
friction free surface for a
displacement of 5 m to the
right.
A 2-kg object is pulled
upward at constant speed by a
20-N force for a vertical
displacement of 5 m.
7.
(6 on page) How much work is done by an applied force to lift a 15-Newton block
3.0 meters vertically at a constant speed?
8.
(7 on page) A student with a mass of 80.0 kg runs up three flights of stairs in 12.0
sec. The student has gone a vertical distance of 8.0 m. Determine the amount of
work done by the student to elevate his body to this height. Assume that her speed
is constant.
9.
A tired squirrel (mass of 1 kg) does push-ups by applying a force to elevate its
center-of-mass by 5 cm. Determine the number of push-ups which a tired squirrel
must do in order to do a mere 5.0 Joules of work.
Click on
10.
Potential Energy
________________ _______________ is the stored energy of position
possessed by an object.
11.
PEgrav = ______________________
PEgrav = _______________
12.
To determine the gravitational potential energy of an object, a ________
______________ _____________________ must first be arbitrarily assigned.
Typically, the ground is considered to be a position of zero height. But this is
merely an arbitrarily assigned position which most people agree upon.
13.
Since the gravitational potential energy of an object is directly proportional to its
height above the zero position, a __________________ of the height will result in
a doubling of the gravitational potential energy. A __________________ of the
height will result in a tripling of the gravitational potential energy.
14.
Give the potential energy at each position.
A
B
C
D
E
_____________
_____________
_____________
_____________
_____________
Click on
15.
Kinetic Energy
_____________ ______________ is the energy of motion. An object which has
motion - whether it be vertical or horizontal motion - has kinetic energy.
16.
_________________________________________
where m = mass of object
v = speed of object
17.
This equation reveals that the kinetic energy of an object is directly proportional
to the square of its speed. That means that for a twofold increase in speed, the
kinetic energy will increase by a factor of __________; for a threefold increase in
speed, the kinetic energy will increase by a factor of __________; and for a
fourfold increase in speed, the kinetic energy will increase by a factor of
__________.
18.
Kinetic energy is a __________ quantity; it does not have a direction. Unlike
velocity, acceleration, force, and momentum, the kinetic energy of an object is
completely described by magnitude alone.
19.
The unit for kinetic energy is the ______________________.
20.
Checking your understanding
1. Determine the kinetic energy of a 1000-kg roller coaster car that is
moving with a speed of 20.0 m/s.
2. If the roller coaster car in the above problem were moving with twice
the speed, then what would be its new kinetic energy?
3. Missy Diwater, the former platform diver for the Ringling Brother's
Circus had a kinetic energy of 15 000 J just prior to hitting the bucket of
water. If Missy's mass is 50 kg, then what is her speed?
Click on
Mechanical Energy
21.
The energy acquired by the objects upon which work is done is known as
___________________ ___________________.
22.
___________________ __________________ is the energy which is
possessed by an object due to its motion or its stored energy of position.
Mechanical energy can be either kinetic energy (energy of motion) or
potential energy (stored energy of position).
Click on
Power
___________________ is the rate at which work is done. It is the work/time ratio.
Mathematically, it is computed using the following equation.
Power = _____________________________
The standard metric unit of power is the _____________. As is
implied by the equation for power, a unit of power is equivalent
to a unit of work divided by a unit of time. Thus, a Watt is
equivalent to a Joule/second. For historical reasons, the
___________________ is occasionally used to describe the
power delivered by a machine. One horsepower is equivalent to
approximately 750 Watts.
1. Two physics students, Will N. Andable and Ben Pumpiniron, are in the
weightlifting room. Will lifts the 100-pound barbell over his head 10 times
in one minute; Ben lifts the 100-pound barbell over his head 10 times in
10 seconds. Which student does the most work? Which student delivers
the most power? Explain your answers.
2. During the Personal Power lab, Jack and Jill ran up the hill. Jack is
twice as massive as Jill; yet Jill ascended the same distance in half the
time. Who did the most work? Who delivered the most power? Explain
your answers.
3. A tired squirrel (mass of 1 kg) does push-ups by applying a force to
elevate its center-of-mass by 5 cm. Determine the number of push-ups
which a tired squirrel must do in order to do a mere 1.0 Joule of work. If
the tired squirrel does all this work in 4 seconds, then determine its power.
4. If little Nellie Newton lifts her 40-kg body a distance of 0.25 meters in
2 seconds, then what is the power delivered by little Nellie's biceps?
Go To
Lesson 2
Internal Forces
External Forces
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1.
Description
KE to PE or PE to KE
of Motion
Explain
A ball falls from a height of 2 meters in the
absence of air resistance.
A skier glides from location A to location B
across the friction free ice.
2.
A baseball is traveling upward towards a man in
the bleachers.
3.
Description
KE to PE or PE to KE
of Motion
Explain
A bungee chord begins to exert an upward
force upon a falling bungee jumper.
4.
5.
The spring of a dart gun exerts a force on a dart
as it is launched from an initial rest position.
Go To Analysis of Situations in Which Mechanical Energy is Conserved
The above demonstrate the
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