ENERGY Part I. Learning Goals for Section 1 The Nature of Energy Distinguish between kinetic and...
-
Upload
conrad-walsh -
Category
Documents
-
view
222 -
download
1
Transcript of ENERGY Part I. Learning Goals for Section 1 The Nature of Energy Distinguish between kinetic and...
Learning Goals for Section 1The Nature of Energy
Distinguish between kinetic and potential energy.
Calculate kinetic energy.Describe different forms of potential energy.Calculate gravitational potential energy.
Work, Power, Efficiency
Work = (Force) (distance) Work measured in Nm
1 Nm = 1 Joule
Power = Work / time Power measured in J/s
1 J/s = 1 Watt1 HP = 764 Watts
Efficiency = (Wout / Win) x 100 Efficiency is a percentage (%)
Work Power Efficiency Problems
Amy uses 20N of force to push a lawn mower 10 meters. How much work does she do?
Frank does 4.8 E4 J of work in climbing a set of stairs. If he climbs the stairs for 2 minutes, what is his power output?
A block and tackle does 1.25 E5 J of useful work, but friction limits the block and tackle to an efficiency of 45%. What is the amount of input on work block and tackle?
Kinetic Energy
energy of motiondepends on mass and speed depends on speed more than it depends on
mass – LOOK AT THE EQUATION!!!
Kinetic Energy Equation
kinetic energy (joules) = ½ mass (kg) × [speed (m/s)]2
KE = ½ mv2
KE Problems
What is the KE of an 8 kg mass at 5 m/s?
What is the mass of an object that has 100 J of KE when moving at 5 m/s?
Determine the velocity of a 6 kg mass has 75 J of KE.
A rocket with a mass of 1.5 E4 kg accelerates at 220 m/s2 for 29s from an initial speed of 5200 m/s. Determine the kinetic energy of the rocket before and after the acceleration.
Potential Energy
stored energystored energy in an object means the object has potential to cause change
Gravitational Potential Energy
stored energy due to positiondepends on both mass and height
Gravitational Potential Energy Equation GPE (J) = mass (kg) × acceleration due to gravity (m/s2) × height (m)
GPE = mgh
remember… mass x acceleration due to gravity = weight
acceleration due to gravity is 9.8 m/s2
GPE Problems
What is the GPE of a 3 kg ball that is 2 m above the floor?
How high do you have to lift a 5 kg box to give it 98 J of GPE?
What is the weight of an stone that has 1200 J of GPE when setting on a 275 m cliff
Elastic Potential Energy
energy stored by something that can stretch or compress – rubber band, spring
PEE = ½ kd2
K is the spring constant for the material Measured in N/m
d is the compression/expansion distance of the material Measured in meters
PEEProblems
The elastic force constant of a spring in a toy is 550 N/m. If the spring is compressed 1.2 cm, compute the potential energy stored in the spring.
The spring constant (k) of a car’s front coil is 1800 N/cm. When the front tire rolls over a rock, the spring is compressed 15 cm from its equilibrium position. How much PEE is stored in the spring?