Energy and Power

COMBINEEnergy – Conservation – Power

Into 1 summary sheet!

Energy is the ability to CHANGE an object. These types of energy are a result of a CHANGE in…….

Work: FORCEKinetic Energy: VELOCITYPotential Energy: HEIGHTElastic Energy: SHAPE

Conservation of Energy

• In a system, the TOTALMECHANICAL ENERGY never changes

• Energy can switch forms, but it cannot be created or destroyed.

KINETIC POTENTIAL ELASTIC

WORK

Examples

No matter type of energy transfer, the set up is the same. Even if there is more than one type of energy

present

TME Initial = TME Final

KE + PE + EE + W = KE + PE + EE + W

Energy: Joules (J)

Work: W = FdKinetic Energy: KE = ½mv2

Potential Energy: PE = mghElastic Energy: EE = ½kx2

Examples

• A ball is dropped from a height of 12m, what is the velocity of the ball when it hits the ground?

Potential Energy Kinetic Energy

Since all of the energy is transferred, we can set them equal to each other

PE = KEm(9.8)(12) = ½(m)v2 mass cancels

15.33 m/s = v

Examples

• A force of 50N pushes horizontally on a 5kg object for a distance of 2m. What is the final velocity of the object?

Work Kinetic Energy

Since all of the energy is transferred, we can set them equal to each other

Work = KE(50)(2) = ½(5)v2

6.32 m/s = v

Sample Problem

•A 5kg cart moving at 2 m/s collides with a spring that has a spring constant of k=5N/m. If all of the cars kinetic energy is transferred into elastic energy, what distance will the spring be compressed?

Answer: 2m

POWER

Power = Energy/ time

P = E/t

On your equation sheet it lists “Energy” as Work for the top of the fraction. But you can put any type of energy on the top part of this

equation.

Sample Problem

•A 50kg man runs up a 5 meter tall stair case in 10 seconds. How much power does her exert in climbing the stairs?

Answer: 245 Watts

Charge Basics and Electrostatic Force

COMBINECharge Basics – Electrostatic Force

Into 1 summary sheet!

Electrostatics:

•Atoms have protons, neutron, and electrons.

•Only electrons can move!

Charge of 1 electron = 1.6E-19 Coulomb (C)

Electrostatics:

•An object becomes charged when its electrons are shifted or transferred

•Extra electrons = (-)•Fewer electrons = (+)

Sample Problem 1:

•An object has a charge of -1.76E-18 C charge. How did the object become charged (gain or lose e-) and how many unbalanced electrons does it have?

Answer: Gained 11 electrons (Show work and explain why)

Electrostatics:

•Two charged objects will feel an Electric Force

•Opposite charges attract (+/-)•Same charges repel (+/+) (-/-)

Electrostatics:

•Calculating the Electric Force

•k = 9E9•q=charge • r= distance between the charges

F e k

q1q2r2

Sample Problem - 2•Calculating the Electric Force

•k = 9E9

What is the magnitude of the electrostatic force between two electrons separated by a distance of 1.00 × 10–8 meter?

221k

r

qqFe

Answer: 2.304 x 10-12 N

Circuits

•A circuit provides a COMPLETE path for electrons to move.

•The flow of electrons is called the current (I).

•Electrons flow because a voltage (V) provides an energy difference

•In order to get energy out of a circuit, there has to be resistors (R).

IRV

Circuits:

IRV Circuits:

Analyze Circuits using an RIVP Table

Units

“Respect Is Very Powerful”

Circuits:

R I V POhms Amps Volts Watts

Series Circuits•A circuit in which there is only one

current path

Circuits:

Series Circuit•Current is the same in all resistors

I = I1 = I2 = I3 = I4

•Voltage is distributed among the resistors

V = V1 + V2 + V3

•Total Resistance is the sum of all resistors.

RT= R1 + R2 + R3

Circuits:

RIVP TABLE!Sample Problem - 1 - Series

•What is the voltage in the 10 ohm resistor?

Parallel CircuitsA circuit in which there are several

current paths

Circuits:

Parallel Circuit•Current is the added in all resistors

IT = I1 + I2 + I3

•Voltage is equal among the resistors

VT = V1 = V2 = V3

•Total Resistance is the reciprocal of all resistors.31/RT = 1/R1 + 1/R2 + 1/R3

Circuits:

RIVP TABLE!Sample Problem - 2 - Parallel