Tuesday May 21

Overview Energy1. Motion2. Object3. Potential4. Mechanical Energy5. Chemical6. Elastic7. Chemical8. Gravitational9. Elastic10.Gravitational

The nature of energy

1. Energy of a spinning bicycle wheel

2. Energy stored in food3. Energy stored in a

boulder on a ….4. Energy stored in a

stretched string5. Energy that is stored

6. Less7. More8. Energy9. Joule10. Potential,kinetic11. Potential12. Chemical

Chapter Test Continued

18) A19) D20) B21) C22) A23) B24) D25) C

Understanding Concepts1. A. PE=mgh=10(9.8)

(1.5)=147 J B. PE=mgh=(10)(9.8)(1)= 98

J2. KE= ½ mv2= .5(10)(10)(10)=

500 J3. KE=PE=147 J

There are two types of potential energy problems.

A 4.5 kg dictionary sits on a 4.0 m high shelf. Find its potential energy.

• PE= mgh• PE= 4.5 (9.8) 4• PE= 176.4 J

A 12-N copper ball sits on a church stepple 40 m above the ground. Find its potential energy.

• PE=WH• PE= 12(40)• PE=480 J

An automobile to be transported by ship is raised 7.0 m above the dock. If its gravitational potential energy is 66000 J, find its mass.

• Given • Solution

An automobile to be transported by ship is raised 7.0 m above the dock. If its gravitational potential energy is 66000 J, find its mass.

• GivenH= 7.0 mA= 9.8 m/s/sPE= 66 000 JM= ?

• Solution• PE=mgh• M=PE/gh• M= 66 000/9.8(7)• M= 960 kg

The world record for pole vaulting is 6.15 m. If the athlete’s

gravitational potential energy is 4,942 J, what is his mass?

• Given • Solution

The world record for pole vaulting is 6.15 m. If the athlete’s

gravitational potential energy is 4,942 J, what is his mass?

• Given• H= 6.15 m• PE= 4942 J• G= 9.8 m/s/s• M=?

• Solution• PE=mgh• M=PE/gh• M= 4942/9.8(6.15)• M= 82 kg

Find the kinetic energy of a .045 kg hockey puck traveling at 45 m/s.

• KE= ½ mv2

• KE= ½ (.045) (45)(45)• KE= 45.56 J

A baseball is pitched with a speed of 35 m/s. Calculate its kinetic

energy if it has a mass of 0.146 kg?

• Given • Solution

A baseball is pitched with a speed of 35 m/s. Calculate its kinetic

energy if it has a mass of 0.146 kg?

• Given• M= 0.146 kg• V= 35 m/s• KE= ?

• Solution• KE= ½ mv2

• KE= (.5)(0.146)(35)(35)• KE= 89 J

A “ping-pong” ball has a mass of .00245 Kg and can be given a

speed of 4.0 m/s. Find its kinetic energy?

• Given • Solution

A “ping-pong” ball has a mass of .00245 Kg and can be given a

speed of 4.0 m/s. Find its kinetic energy?

• Given• M= 0.00245kg• V= 4 m/s• KE= ?

• Solution• KE= ½ mv2

• KE= (.5)(0.00245)(4)(4)• KE= 0.0196 J

Potential Energy Worksheet

• 1. PE=mgh or PE=WH• 2. Joule (J)

3. PE=WHPE=12(21)PE=252 J

Potential Energy Worksheet

4. PE=WHPE=79(20)PE= 1580 J

5.PE=WHPE=190(45)PE=8550 J

Potential Energy Worksheet

6.PE=WHPE= 966(72)PE= 69, 552 J

7.PE=mghPE=5(9.8)12)PE= 588 J

Kinetic and Potential Energy Worksheet

1 KE= ½ mv2

• KE= ½ 2.1(30*30)• KE= 945 J

3 KE= ½ mv2

• KE= ½ (1120) 40 * 40• KE= 8,960,000 J

Kinetic and Potential Energy Worksheet

7. D8. A9. D10.Friction.

Energy problems Worksheet

• 1. KE= ½ mv2

• KE= = .5(3) (5)(5)

• KE= 37.5 J

Energy problems Worksheet

• 2. PE=mgh• PE= 6.5(9.8)(5)• PE=166 J

Energy problems Worksheet

• KE= ½ mv2

• M= 2 KE/v2• M= 2(173)/(3.8 * 3.8)• M= 24 J

Energy problems Worksheet

• PE=mgh• H=PE/mg• H=328/(7.5)(9.8)• H=4.5m

Energy problems Worksheet

• 5.• KE= ½ mv2

• KE= ½ 30 (2*2)• KE= 60 J• KE= ½ mv2

• KE= ½ 60 (2*2)• KE= 120 J• It doubles.

Energy problems Worksheet• 6. • KE= ½ mv2

• KE= ½ 30 (2*2)• KE= 60 J• KE= ½ mv2

• KE= ½ 30 (4*4)• KE= 240 J• It is quadrupled.

•

Energy problems Worksheet

• 7.PE= mgh PE= 4(9.8)(2) PE=78.4 J J PE=mgh PE= 4(9.8)(4) PE= 156.8 J

It doubled.

Energy problems Worksheet

• 8.• KE= ½ mv2 . 4.2 m/s

• KE= ½ 12 (3*3)

Energy problems Worksheet

• 9.• KE= ½ mv2

• 2KE= m (52*52)• m= 72 kg

Energy problems Worksheet

10. PE= mgh PE= 0.49(9.8)(3.6) PE=17.3 J PE=mgh PE= 0.49(9.8)(1.5) PE= 7.2 J Decreased by 10.1 J