Download Kinetic Energy

Energy
Energy: this is the capacity of a physical system to do work.
Work is done when energy is transferred.
Mechanical Energy: this is the energy that is possessed by an
object, due to its motion or its stored energy of position.
Potential Energy: this is the energy stored in a system which
could be used to do work.
Conservation of Energy: Energy is neither created nor
destroyed but is simply transformed (changes form) and/or
transferred to another body.
Forms of energy:
Form of energy
Radiant
Description
Examples include visible light, x-rays, light
waves from the sun
Thermal
(heat energy) results from the motion
(vibration) of particles in a substance
Electrical/magnetic Results from the forces of repulsion and
attraction of charged particles causing
electrons to move
Nuclear
Energy stored in the nucleus of the atom
Sound
Vibrational waves
Chemical potential Stored in materials such as fuel and food
Gravitational
Energy is stored in a system due to its
potential
position in relation to a gravitational field
Kinetic
Energy of motion
Elastic potential
Energy stored in a stretched or compressed
object such as a spring, or catapult
Kinetic Energy:
Consider a net force acting on a mass. According to Newton’s
second law, the net force produces an acceleration. If there is
an acceleration, then there must be an initial velocity, v1 and a
final velocity v2.
Using the formulas f = ma and 𝑣22 = 𝑣12 + 2𝑎𝑑, derive an
equation for kinetic energy:
𝐾𝐸 =
1
𝑚𝑣 2
2
m is the scalar quantity mass measured in kg
v is the scalar quantity speed measured in m/s
Where KE is scalar quantity kinetic energy measured in Joules
(J)
Example 1) calculate the kinetic energy of a baseball that is 142
g and travelling at 40 m/s [south]
The Work-Energy Theorem
The quantities of energy and work are very closely tied
together. If there is a transfer of energy, then work has been
done.
Work-energy theorem: when a net force does work, W, on an
object, the kinetic energy of the object changes from its initial
value KE1 to a final value of KE2, the difference between the two
values is Work.
W = ΔKE
So
Or
𝑊 = 𝐾𝐸2 − 𝐾𝐸1
Or
𝑊=
1
1
𝑚𝑣22 − 𝑚𝑣12
2
2
Example 2) A space probe of mass 5.00 x 104 kg is travelling at
a speed of 1.10 x 104 m/s through deep space. No forces act on
the probe except that generated by its own engine. The engine
exerts a constant external force of 4.00 x 105 N directed parallel
to the displacement. The engine fires continually while the
probe makes a straight line for a displacement of 2.50 x 106 m.
Determine the final speed of the probe.
Learning Activity 4.2: Kinetic Energy and the Work-Energy Theorem
1. Determine the changes(transformation and transfer of) in energy for each situation:
a. A microwave oven cooks a pot roast starting with the electrical energy transferred
into the system.
b. Your arm lifts a weight above your head, starting with chemical energy
c. A watch’s spring is fully wound.
d. A solar panel heats the water for a swimming pool.
e. Dammed water is used to generate electricity.
f. Turning on a flashlight (starting with the battery)
2. Determine the kinetic energy of an elephant with a mass of 2000 kg is running at 5 m/s.
3. An object is moving at 9 m/s and has 215 J of kinetic energy. What is the mass of the
object?
4. An automobile of mass 1250 kg starts from rest. It accelerates under a net force of 3250
N [west] over 25 m. Calculates the final kinetic energy and the final velocity of this
automobile.
5. A curling rock of mass 20 kg is sliding along the ice with a velocity of 2.75 m/s [east].
During the next 3 seconds, the curling rock slows to a velocity of 1.5 m/s [east] while
sliding 6.38 m [east]
a. Calculate the change in kinetic energy of the curling rock
b. Calculate the net force that was acting on the curling rock
c. The coefficient of kinetic friction between the curling rock and the ice.
6. The hammer throw is a track and field event in which a 7.3 kg ball (the hammer), starting
from rest is whirled around in a circle several times and released. It then moves upward
on the familiar curving path of a projectile motion. In one throw, the hammer is released
with an initial speed of 29 m/s. Determine the work done to launch the hammer.
7. Katniss fires a 75 g arrow horizontally at a squirrel. The bowstring exerts an average
force of 65 N on the arrow over a distance of 0.9 m. With what speed does the arrow hit
the squirrel?
8. A 65 kg jogger is running at a speed of 5.3 m/s
a. What is the kinetic energy of the jogger?
b. How much work is done to accelerate the jogger
c. 5.3 m/s from rest?
9. The speed of a hockey puck decreases from 45 to 44.67 m/s across a 16 m surface of
ice. Find the coefficient of kinetic friction between the puck and the ice.
Energy
Energy: this is the capacity of a physical system to do work.
Work is done when energy is transferred.
Mechanical Energy: this is the energy that is possessed by an object, due to its motion or its
stored energy of position.
Potential Energy: this is the energy stored in a system which could be used to do work.
Conservation of Energy: Energy is neither created nor destroyed but is simply transformed
(changes form) and/or transferred to another body.
Forms of energy:
Form of energy
Description
Examples include visible light, x-rays, light waves from the sun
(heat energy) results from the motion (vibration) of particles in a substance
Results from the forces of repulsion and attraction of charged particles
causing electrons to move
Energy stored in the nucleus of the atom
Vibrational waves
Stored in materials such as fuel and food
Energy is stored in a system due to its position in relation to a gravitational
field
Energy of motion
Energy stored in a stretched or compressed object such as a spring, or
catapult
Kinetic Energy:
Consider a net force acting on a mass. According to Newton’s second law, the net force
produces an acceleration. If there is an acceleration, then there must be an initial velocity, v 1
and a final velocity v2.
Using the formulas f = ma and 𝑣22 = 𝑣12 + 2𝑎𝑑, derive an equation for kinetic energy:
𝐾𝐸 =
1
𝑚𝑣 2
2
m is the scalar quantity mass measured in kg
v is the scalar quantity speed measured in m/s
Where KE is scalar quantity kinetic energy measured in Joules (J)
Example 1) calculate the kinetic energy of a baseball that is 142 g and travelling at 40 m/s
[south]
The Work-Energy Theorem
The quantities of energy and work are very closely tied together. If there is a transfer of energy,
then work has been done.
Work-energy theorem: when a net force does work, W, on an object, the kinetic energy of the
object changes from its initial value KE1 to a final value of KE2, the difference between the two
values is Work.
So
W = ΔKE
Or
𝑊 = 𝐾𝐸2 − 𝐾𝐸1
Or
𝑊=
1
1
𝑚𝑣22 − 𝑚𝑣12
2
2
Example 2) A space probe of mass 5.00 x 104 kg is travelling at a speed of 1.10 x 104 m/s
through deep space. No forces act on the probe except that generated by its own engine. The
engine exerts a constant external force of 4.00 x 105 N directed parallel to the displacement.
The engine fires continually while the probe makes a straight line for a displacement of 2.50 x
106 m. Determine the final speed of the probe.