Section+9

=Section 9- Conservation of Energy: Defy Gravity=

toc

What Do You See?
1/31/11 page 234

The guy does a triple axil in the air and is spinning just like the helicopter next to its choppers are.

What Do You Think?
1/31/11 page 234

No and no, you would need to jump high and spin really fast.

Investigate
1/31/11 page 234

1a. 20 b. 6.6s c. yea 2a. 31(.33)= 10.23 b. yes, hang time is the time in the air 3. w= 547.5 N m= 55.87 kg 4a. 33 cm 5a. 97 cm b. 64 cm 6a. 129 cm b. 96 cm

Physics Talk
1/31/11 page 237

When you are jumping, when you are in the ready position you have elastic potential energy. Potential energy is present due to chemical reactions in muscles and as you move EPE exchanges to GPE. Conservation of energy can be described as EPE, Ke, GPE, sound energy, light energy, chemical energy, electrical energy, nuclear energy, internal energy

Checking Up
1/31/11 page 241

1. Energy in the launch position comes from chemical reaction in the muscles 2. In the launch position the student will have an increase GPE and increase KE. In the peak of the jump they will lose KE and gain GPE. 3. sound energy, light energy, chemical energy, electrical energy, nuclear energy, internal energy

Physics Plus
2/3/11 page 242

m= 50g= .05 kg h= 45 cm and 28 cm

calculate GPE KE E total and V ignore all forms of friction- energy is conserved

A. GPE=mgh GPE= (.050)(9.8)(.45) GPE= .22 J

KE=1/2mv^2 KE= (1.2)(.050)(0^2) KE= 0 J

Et=KE+GPE Et= .22 J

V=0m/s at top of ride

B. GPE= mgh GPE= (.050)(9.8)(0) GPE= 0 J

KE= Et-GPE KE= .22-0 KE= .22 J b/c Et is constant

Et= .22 J b/c Et is conserved

KE=1/2mv^2 .22=1/2(.050)v^2 V=2.9m/s

C. GPE= mgh GPE= (.050)(9.8)(.28) GPE= .137 J

KE= Et-GPE KE= .22- .137 KE= .083

Et= .22 J

KE=1/2mv^2 .083= 1/2(.050)v^2 V= 1.8 m/s

Physics To Go
2/4/11 page 244

1. w=fd w= m*a*d w= 50(9.8)(1) w= 490 J 2. work, kinetic energy, work 3. looking at the jump & seeing if he flloats 4. 5. jump faster & use more KE 6a. w=1(1) w= 1 J b. w=(1)(10) w= 10 J c. w=(10)(1) w= 10 J d. w= (.1)(100) w= 10 J e. w= (100)(.1) 7a. GPE is the same thing as work GPE= 1J b. GPE= 10J c. GPE= 10J d. GPE= 10J e. GPE= 10J 8a. GPE is the same as KE because they are conserved at the top and the bottom KE= 1J b. KE= 10J c. KE= 10J d. KE= 10J e. KE= 10J 9. w= (50)(43) w= 2150 J 10. KE= .5(62)(8.2)^2 KE= 2084.44 11a. F=MA 30=5A A= 6 m/s^2 b. W= 30(18.75) w= 562.5 J 12a. 40000=3200 d d= 12.5 m b. 3200=1200A A= 2.66 m/s/s 13. w= (1/2)(.15)(40)^2 w= 120 J 14.