1-4 Notes and Problems

Chapter 4 105-169

What is energy?

*Change requires energy*

Kinetic energy-

the energy a moving object has because of its motion(Energy in motion.)

Potential energy-

stored energy due to an object’s position

(Energy due to position or composition.)

A) Elastic potential energy-

energy stored by something that can stretch or compress, such as a rubber band or a spring

B) Chemical potential energy-

energy stored in chemical bonds

C) Gravitational potential energy (GPE) - energy stored by objects due to their position above Earth’s surface

Mechanical energy-

the total amount of potential and kinetic energy in a system

Law of conservation of energy-

This states that energy cannot be created nor destroyed only changed from one form to another.

*Law of conservation of mass-

This states that mass cannot be created nor destroyed only changed from one form to another.

*Law of conservation of mass and energy- This states that energy and mass cannot be created nor destroyed only changed from one form to another.

E=mc2

Work: the transfer of energy to an object by a force that makes an object move in the direction of the force.

Chapter 4 Equations

1.What is the mechanical energy of a 4000 Kg that is 1000 m up a mountain, going at 10 m/s?

ME= (PE=mgh)  +   (KE= ½ mass *(v2) )

ME=4000Kg(10 m/s2)(1000m)+1/2(4000Kg)(10 m/s) 2

ME= 40,000,000 J+  200,000 J

ME= 40,200,000 J

 2.What is the kinetic energy of a 500 g ball that is traveling at 20 m/s?

KE= ½ mass *(v2)

*convert grams to Kilograms  500/1000= 0.5Kg

KE=1/2(0.5 Kg)(20 m/s) 2

KE= 100 J

 3.What is the potential energy of a 300 Kg rock perched 10 Km above the valley floor?

PE=mgh

*convert Km to meters  10*1000=10,000 m

PE= 300 Kg(10 m/s2)(10,000 m)

PE= 30,000,000 J

 4. How long will it take for a 200 m pendulum to swing 8 times?

T = 2л√L/g

     T=6.28√(200/10)

     T=6.28(4.5)=28.37 sec (This is the time for one swing or tick.)

     T=28.37 sec(8)=226.96 sec.(This is the time for all 8 swings or ticks.)

1.       What is the PE of a 500 Kg object 20 Km above the surface?

2.       What is the Kinetic energy for a 400 Kg object traveling at 2 Km/second?

3.       How many seconds will it take a tire swing to go back and forth 6 times (12 ticks) if the chain is 3 m long?

Answers below

1. What is the PE of a 500 Kg object 20 Km above the surface?

•          Use the Potential energy formula.

•          PE=mgh

•          Convert Km to m.  20 km = 20,000 m

•          Place data in the formula.

•          PE= 500 Kg(20,000 m)(10 m/s2)

•          PE= 100,000,000 J

2. What is the Kinetic energy for a 400 Kg object traveling at 2 Km/second?

•          Use the Kinetic energy formula.

•          KE= 1/2mv2

•          Place data in the formula.

•          KE= 1/2(400 Kg)(2,000 m/s)2

•          KE= (200 Kg)(4,000,000 m2/s2)

•          KE= 800,000,000 J

3.How many seconds will it take a tire swing to go back and forth 6 times (12 ticks) if the chain is 3 m long?

•          Determine the formula.

•          T= 2 л √L/g

•          Plug in information.

•          T= 6.28 √ 3m/9.8m/s2

•          T= 6.28 √0.3 s2

•          T= 6.28 (0.55 sec)

•          T= 3.47 sec (12 swings)=41.7 sec

1.       What is the PE of a 40,000 g object 20 m above the surface?

2.       What is the Mechanical energy for a 400 Kg object traveling at 2 m/second and 1 Km above the Earth?

3.       How many seconds will it take a tire swing to go back and forth 4 times (8 ticks) if the chain is 8 m long?

Answers below

1. What is the PE of a 40,000 g object 20 m above the surface?

•          Use the Potential energy formula.

•          PE=mgh

•          Convert g to Kg. 40,000 g = 40 Kg

•          Place data in the formula.

•          PE= 40 Kg(9.8 m/s2) (20m)

•          PE= 7840 J

2. What is the Mechanical energy for a 400 Kg object traveling at 2 m/second and 1 Km above the Earth?

•          Use the Kinetic energy formula.

•          KE= 1/2mv2

•          Place data in the formula.

•          KE= 1/2(400 Kg)(2 m/s)2

•          KE= 800 J

•          PE=mgh

•          PE= (400 Kg)(10 m/s2) (1,000 m)

•          PE= 4,000,000 J

•          4ME=4,000,800 J

3. How many seconds will it take a tire swing to go back and forth 4 times (8 ticks) if the chain is 8 m long?

•          Determine the formula.

•          T= 2 л √L/g

•          Plug in information.

•          T= 6.28 √ 8m/9.8m/s2

•          T= 6.28 √0.3 s2

•          T= 6.28 (0.55 sec)

•          T= 3.47 sec (8 swings)=45.39 sec

1.       What is the weight in Newtons of an object on earth that is 10,000 g?

2.       What is the PE of a 500 Kg object 20 Km above the surface?

3.       What is the Kinetic energy for a 400 Kg object traveling at 2 Km/second?

4.   What is the mechanical energy if the Potential energy is 200 Joules and the Kinetic energy is 4500Joules?

5.   What is the weight in Newtons of an object on earth that is 60 Kg?

1. What is the weight in Newtons of an object on earth that is 10,000 g?

•          Determine the formula.

•          F=ma

•          Convert g to Kg

•          10,000g /1000 g/1 Kg = 10 Kg

•          Plug in information.

•          F= 10 Kg(9.8 m/sec2)

•          F= 98 N

2. What is the PE of a 500 Kg object 20 Km above the surface?

•          Use the Potential energy formula.

•          PE=mgh

•          Convert Km to m.  20 km = 20,000 m

•          Place data in the formula.

•          PE= 500 Kg(20,000 m)(9.8 m/s2)

•          PE= 98,000,000 J

3. What is the Kinetic energy for a 400 Kg object traveling at 2 Km/second?

•          Use the Kinetic energy formula.

•          KE= 1/2mv2

•          Place data in the formula.

•          KE= 1/2(400 Kg)(2,000 m/s)2

•          KE= (200 Kg)(4,000,000 m2/s2)

•          KE= 800,000,000 J

4. What is the mechanical energy if the Potential energy is 200 Joules and the Kinetic energy is 4500Joules?

•          Determine the formula.

•          ME = PE + KE

•          Plug in information.

•          ME= 200 J + 4500 J= 4700 J

5. What is the weight in Newtons of an object on earth that is 60 Kg?

•          Determine the formula.

•          F=ma

•          Plug in information.

•          F= 60 Kg(9.8 m/sec2)

•          F= 588 N

1.       What is the weight in Newtons of an object on earth that is 50,000 g?

2.       What is the PE of a 300 g object 5 Km above the surface?

3.       What is the Kinetic energy for a 80 Kg object traveling at  60 m/s?

4.       What is the mechanical energy if the Kinetic energy is 4500 Joules and the Potential Energy is 3500 Joules?

5.       How long will it take for a pendulum with a length of 60 meters  to swing 4 times on the earth?

1. What is the weight in Newtons of an object on earth that is 50,000 g?

•          Determine the formula.

•          F=ma

•          Plug in information.

•          Convert 50,000 g/1000 g/1Kg= 50

•          F= 50 Kg(9.8 m/sec2)

•          F= 490 N

2. What is the PE of a 300 g object 5 Km above the surface?

•          Use the Potential energy formula.

•          PE=mgh

•          Convert 300 g/1000 = 0.3 Kg

•          Convert 5 Km * 1000 m/1Km= 5000 m

•          Place data in the formula.

•          PE= .3 Kg(5000 m)(9.8 m/s2)

•          PE= 14,700 J

3. What is the Kinetic energy for a 80 Kg object traveling at  60 m/s?

•          Use the Kinetic energy formula.

•          KE= 1/2mv2

•          Place data in the formula.

•          KE= 1/2(80 Kg)(60 m/s)2

•          KE= (40 Kg)(3600 m2/s2)

•          KE= 144,000 J

4. What is the mechanical energy if the Kinetic energy is 4500 Joules and the Potential Energy is 3500 Joules?

•          Determine the formula.

•          ME = PE + KE

•          Plug in information.

•          ME= 3500 J + 4500 J= 8000 J

5. How long will it take for a pendulum with a length of 60 meters  to swing 4 times on the earth?

•          Determine the formula.

•          T = 2л√L/g

•          Plug in information.

•          T = 2(3.14)(√60/9.8)

•          T= 6.28(2.47)

•          T= 15.54

•          T= 15.54(4) =62.16 Sec

1.       What is the weight in Newtons of an object on earth that is 30 Kg?

2.       What is the PE of a 4,000 g object 50 m above the surface?

3.       What is the Kinetic energy for a 1,200 g object traveling at 3,000 m/s?

4.       What is the mechanical energy if the the Kinetic energy is 4500 Joules and the object has a mass of 2,000 Kg and is 20 m above the Earth?

5.       What is the weight in Newtons of an object on earth that is 100 g?

1. What is the weight in Newtons of an object on earth that is 30 Kg?

•          Determine the formula.

•          F=ma

•          Plug in information.

•          F= 30 Kg(9.8 m/sec2)

•          F= 294 N

2. What is the PE of a 4,000 g object 50 m above the surface?

•          Use the Potential energy formula.

•          PE=mgh

•          Place data in the formula.

•          PE= 4 Kg(50 m)(9.8 m/s2)

•          PE= 1960 J

3. What is the Kinetic energy for a 1,200 g object traveling at 3,000 m/s?

•          Use the Kinetic energy formula.

•          Convert g to Kg

•          1200g /1000 g/1 Kg = 1.2 Kg

•          KE= 1/2mv2

•          Place data in the formula.

•          KE= 1/2(1.2 Kg)(3,000 m/s)2

•          KE= (0.6 Kg)(9,000,000 m2/s2)

•          KE= 5,400,000 J

4. What is the mechanical energy if the the Kinetic energy is 4500 Joules and the object has a mass of 2,000 Kg and is 20 m above the Earth?

•          Determine the formula.

•          ME = PE + KE

•          Plug in information.

•          PE=mgh

•          PE=2000 Kg(9.8)(20m)= 392,000 J

•          ME= 392,000 J + 4500 J= 396,500 J

5. What is the weight in Newtons of an object on earth that is 100 g?

•          Determine the formula.

•          F=ma

•          Plug in information.

•          Convert mass to Kg 100g=0.1 Kg

•          F= 0.1 Kg(9.8 m/sec2)

•          F= 0.98 N