Monday, December 19, 2016
Activity 69: Energy Practice Problems
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
Activity 68: Energy Questions
Please answer these questions on page 260 on the textbook.
13, 15, 18, 20, 21
When you are done check your answers here..
Tuesday, December 13, 2016
Monday, December 12, 2016
Activity 69: Springs Pendulums & Power Questions
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
Activity 67: Energy Notes
Energy Notes
Total Work = Fd Cos(θ)
KE = ½ mv2
Wnet = ΔKE = Δ½ mv2 = FnetdCos(θ)
PE = Potential Energy
ΔPE = mgh
Conservative Forces
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
Nonconservative forces:
KEi + PEi + Wnc = PEf + KEf
Wnc = ΔKE + ΔPE
Conservation of Energy
Other forms of energy -> electric, chemical, radiant, nuclear & thermal.
KEi + PEi + Wnc + OEi = PEf + KEf + Oef
1 kcal = 4184 joules
Power
Power is the rate at which work is done.
Power = Work/Time = Fd Cos(θ)/Time
Units in Watts.
1 Watt= 1 J/s
1hp = 746 Watts
1hp = 746 Watts
Link to Gravitational Potential Energy Questions
Friday, December 9, 2016
Thursday, December 8, 2016
Activity 65: Introduction to Work
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
or
PEi + KEi = PEf + KEf
Read section 7.1 and answer questions 1 -> 8 on page 260. Review your answers here.
Tuesday, December 6, 2016
Activity 45: 2 Body Problem Answers
Q1: a = 4.46m/s/s
Force = 7160N
Q2: a = 1.32 m/s/s
Force = 15.8N
Q3: a = .215 m/s/s
Ft = 1811N
Q4: A to B Force = 316N
C to D Force = 276 N
Friday, December 2, 2016
Activity 43: Forces in Motion PS #3
Pick up a paper copy of Forces in Motion Problem Set #3. When you are done check your answers here....
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