## Monday, December 19, 2016

### Activity 69: Energy Practice Problems

Energy Practice Problems

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

13, 15, 18, 20, 21

Warm-Up

## 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

22, 23, 27,

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.

Units in Watts.

1 Watt= 1 J/s

1hp = 746 Watts

## Friday, December 9, 2016

Read Sections 7.2, 7.3, 7.4 & 7.5 in the textbook

## 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

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

## 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