PE, KE, AND TE DIAGRAMS AND HOW

TO CALCULATE KINETIC ENERGY

Solving Energy Problems

pg 299 (1-4)

m = PE h = PE

g*h g*m

kilo hecto  deka  gram 

deci  centi  milli 

kg hg dg g dg cg mgkilogra

mhectogra

mdekagra

m gramdecigra

mcentigra

mmilligr

am

1,000 100 10 1 0.1 0.01 0.001

MASS

Answers to PE calculations

(1.a) PE = 493,920J or…4.9 x 105J

(1.b) PE = 5,605,600J or…5.6 x 106J

(1.c) PE = 2802.8J or..2.8 x 103J

(2.) PE = 1.4 x 1015J(3.) h=14.84m

(4.) m= 57.82kg

Calculating PE• Which apple has more

PE?• Apples have a mass=

1.5kg• Apple “A” height= 15m• Apple “B” height= 20m• Remember PE=mgh• So…• Apple “A” PE= 220.5J• Apple “B” PE= 294 J• So the winner is…Apple

“B”• Spectrum pg 698 (96-

100)

Apple “A”

Apple “B”

15m

20m

Mass of apples = 1.5kg

PE CalculationsPE

1. PE= 6856.08J2. m= 4.6 kg3. h= 19.18m4. PE=7763.8J5. m=.348 kg 6. h= 24.7 m

Answers to PE calculationspg 698 (96-100)

96. PE= mgh (0.14kg)(9.8m/s2)(3.5m)PE=4.8J

97.h= PE/mg 6.6 J/ (74kg)(9.8m/s2)h=.0091m

98. PE=mgh (67kg)(9.8m/s2)(2.04m) PE=1339.4J or 1.3x103J

99. m= PE/gh 88.9J/ (2.0m)(9.8m/s2)m=4.5kg

100. h= PE/gm .744 J/ (.23kg)(9.8m/s2)m= .33m

Total EnergyRemember…Total Energy is all the energy in a

systemRemember the formula?

TE=PE +KE+ HeatThe heat in a system is the…

FRICTION!Total Energy will equal the GPE at the highest

point in system.Total Energy NEVER changes in a system!

Because…what you put in is what you get out!

Let’s see if it works…

Set up a Data TablePE KE TE

A= A= A=

B= B= B=

C= C= C=

D= D= D=

E= E= E=

Let’s PracticeA

E

B

C

D

Calculate the PE, KE and TE of the ball at the 5 positions. Assume there is no

frictionThe mass of the ball is 8kg.

Height = 200m

Height = 0m

Draw this picture and label it!

Set up a Data TablePE

A= 15680J

B= 11760J

C= 7840J

D= 3920J

E= 0J

TEA= 15680J

B= 15680J

C= 15680J

D= 15680J

E= 15680J

KEA= 0J

B= 3920J

C= 7840J

D= 11760J

E= 15680J

Bungee Jumper CalculationsPerson’s mass = 2kg

For A-E calculate on white boards:

PE, KE, and TE (assume NO friction)

Draw the picture and label it. Set up another data table!

PE, KE, and TE Calculations

PEA.

1960J

B.1470J

C.980J

D.490J

E. 0J

KEA. 0J

B. 490J

C. 980J

D. 1470J

E. 1960J

TEA. 1960J

B. 1960J

C. 1960J

D. 1960J

E. 1960J

3. Two ice skaters, a man and a woman, are involved in a doubles skating competition. At one point both skaters are moving at the same speed next to one another. The man is twice as massive as the woman. Carefully read each of the following statements about the scenario and write down the statement you agree with. Explain your thinking.

1. Both skaters have the same KE since they are moving at the same speed.

2. The mass of the skaters is more important than the speed of the skaters in determining their KE.

3. Skater A has more KE since she is only half the mass of skater B.

4. Skater B has more KE since he is twice as massive as skater A

5. If Skater A doubles her speed, she will have the same KE as Skater B.

KINETIC Energy (KE)Kinetic Energy (KE) is the energy of any

moving object.

KE depends on the mass and the velocity (speed) of an object. Only ½ of the mass is used, but velocity is squared… so KE depends mostly on the velocity of the object.

KE = ½m * v2

Units are Joules!!! (J)

Speed vs. Velocity

What’s speed?How fast an object is moving.

Then what is velocity?Velocity is speed with direction!Ex. Traveling 90 m/hr north bound.

Solving KE Problems

KE = ½ m * v2

***Remember PEMDAS (order of operations)

1ST: Square the v 2nd: Take half the mass3rd: Multiply 1/2m * v2

Page 301 (1a. & 1b.)