Monday, December 19, 2016
Energy Practice Problems
Please answer the following question in this document. The answer key is on the last page.
While all the questions are good, you might want to focus on the following ones first.
3, 5, 8, 10, 11, 13, 14, 17, 18, 21, 23, 24, 27, 29, 30, 34, 38, 40, 41, 42, 45, 46, 47 , 48, 49, 50, 53, 54, 58, 60, 63, 64, 69, 70, 71, 74
Wednesday, December 14, 2016
Tuesday, December 13, 2016
Monday, December 12, 2016
Speed of a Pendulum
A pendulum consists of a ball at the end of a massless string of length 1.4 m. The ball is released from rest with the string making an angle of 20 degrees with the vertical. What is the maximum speed of the pendulum?
Potential Energy of a Spring
PEs = ½ kx2
Please answer these questions on page 260 on the textbook.
22, 23, 27,
When you are done check your answers here..
24, 25, 32, 33, 37, 38
Total Work = Fd Cos(θ)
KE = ½ mv2
Wnet = ΔKE = Δ½ mv2 = FnetdCos(θ)
PE = Potential Energy
ΔPE = mgh
A “Conservative Force” is once for which work depends only on the starting point and ending point.
We can define potential energy for any conservative force.
PEg = mgh
PEs = ½ kx2
Mechanical Energy = KE + PE
Conservation of Mechanical Energy
When only conservative forces act then:
KEI + PEI = KEf + PEf
Or KE + PE = constant
KEi + PEi + Wnc = PEf + KEf
Wnc = ΔKE + ΔPE
Conservation of Energy
Other forms of energy -> electric, chemical, radiant, nuclear & thermal.
Friday, December 9, 2016
Thursday, December 8, 2016
Work = Fd cos(theta)
F = Applied Force
d = the displacement of the object
theta = the angle between the Applied Force the the Direction of movement
Work is measured in Joules.
1 Joule = 1 Newton meter = 1 kg m^2/s^s
1 J is small. ~ lifting a 100 gram apple 1 meter.
Other energy measures: 1 calorie = energy need to heat 1 g of water by 1 degree Celsius
1 calorie = 4.184 J
1 food calorie (kcal) = 4185 J
Work is the means of energy transfer.
Net Work is the sum of all work done on a system: Wnet = Fnet d cos(theta)
Net Work is the area under a Net Force vs Displacement Graph.
If the Fnet is in the same direction as the motion then Wnet = Fnet d
Since Fnet = mad
Wnet = mad
v^2 = v0^2 + 2ad
a = (v^2 - v0^2)/(2d)
Wnet = m( (v^2 - v0^2)/(2d)) (d)
Wnet = 1/2 mv^2 - 1/2 mv0^2
1/2 mv^2 = KE
Wnet = change in KE of the system
If Wnet is zero then there is no change in kinetic energy.
2 kinds of Mechanical energy
KE = 1/2mv^2
PE = mgh
Conservative Forces: A force is conservative depends on the starting point and ending point of an object.
NonConservative Forces: A force whose work depends on the path taken. Friction is a good example.
Conservation of of Mechanical Energy
When on conservative forces are involved:
Wnet = 1/2 mv^2 - 1/2mv0^2 = delta KE
Wnet = delta KE
-deltaPE = delta KE
PEi + KEi = PEf + KEf
Read section 7.1 and answer questions 1 -> 8 on page 260. Review your answers here.