Physics chapter 11

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1
Work
Work-
- Energy Theorem
Energy Theorem
& Thermal Energy
& Thermal Energy
Work
Work –
– Energy Theorem
Energy Theorem
y The work applied to a system is equal to
the change in energy of that system,
g gy y ,
where the change in energy can include
kinetic energy, potential energy
(gravitational or elastic), and/or thermal
energy (e.g., energy losses due to
friction).
f
y In equation form:
W E
applied to a system system
= Δ

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Example
Example
y A car of mass 1500.0 kg accelerates from
20 0 m/s to 30 0 m/s Calculate the work
20.0 m/s to 30.0 m/s. Calculate the work
required for this acceleration.
Example 2
Example 2
y 6 000 000 000 J of work is done to
accelerate a 50 000 kg airplane from rest
accelerate a 50 000 kg airplane from rest.
What is its final speed?

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Thermal Energy
Thermal Energy
y is heat energy, internal energy related to
the motion of atoms
the motion of atoms.
y Friction produces thermal energy
y Where:
◦ E is thermal energy (J)
E F d
th kf
= • Δ
◦ Eth is thermal energy (J)
◦ Fkf is the force of kinetic friciton (N)
◦ Δd is the distance (m)
Example 3
Example 3
y A skater of mass 35 kg glides on level ice,
experiencing a coefficient of kinetic
experiencing a coefficient of kinetic
friction of 0.10. If she glides 20.0 m,
calculate the amount of thermal energy.

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Today’s Task
Today’s Task
1. A toy car with a mass of 2 kg starts at rest.
A spring performs 196 joules of work on the
p g p j
car. What is the toy car’s final velocity?
2. A wagon with an initial velocity of 4 m/s
and a mass of 35 kg gets a push with 350
joules of force. What is the wagons final
velocity?
3. A skateboarder with a mass of 30 kg ends
up with a final velocity of 7 m/s after a push
of 360 joules of work. What was the
skateboarders initial velocity?