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..


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







Link to Gravitational Potential Energy Questions








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