Vật Lí 9 Bài 60: Định luật bảo toàn năng lượng – Giải bài tập SGK Vật Lí 9 Bài 60

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Physics 9 Lesson 60: The Law of Conservation of Energy, compiled by Le Hong Phong High School, hopes to provide useful documents to help students master the lesson knowledge and achieve good results in the above tests and reviews. class.

Summary of Physics 9 Lesson 60

Energy transformation in mechanical, thermal and electrical phenomena.

a) Convert potential energy into kinetic energy and vice versa. Loss of energy

In mechanical processes, mechanical energy is always reduced, the lost mechanical energy has been converted into heat energy. If the increased mechanical energy of an object is due to the object outside the distribution system, if it is lost, it is transferred to another object.

For example:

Drop the ball on the slide from point A with height h1.

When the ball rolls from position A to position C: Potential energy is converted into kinetic energy.

When the ball rolls from position C to position B: Kinetic energy is converted into potential energy.

The potential energy of the marble at position A is greater than the potential energy of the marble at position B, this means that part of the energy has been lost (converted into heat due to friction with the slide) ⇒Mechanics conversion into heat energy.

b) Convert mechanical energy into electrical energy and vice versa. loss of mechanical energy

In generators, mechanical energy can be converted into electrical energy, and in electric motors most of the electrical energy is converted into mechanical energy.

– The final part of the useful energy is always smaller than the initial energy distributed to the machine.

– The lost energy has been converted into another form of energy.

For example:

1

The generator and the electric motor are connected by wires, the two weights are of the same size and weight.

Raise the weight to h1 then release ⇒ the left weight moves from top to bottom ⇒ the generator works ⇒ generates electricity ⇒ the electric motor rotates ⇒ the right weight goes up to the height h2.

When the left mass falls, only part of the potential energy is converted into electrical energy and a part is converted into kinetic energy of the weight itself. When the current is to rotate the electric motor to pull the right weight up, only part of the electrical energy is converted into mechanical energy, and part of the electrical energy is converted into heat energy to heat the conductor.

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Principle of conservation of energy

Energy is neither created nor destroyed, but only transformed from one form to another, or transferred from one object to another.

Solve the exercises in the Physics textbook 9 Lesson 60

Lesson C1 (page 157 Physics Textbook 9)

Show how the potential and kinetic energy of the marble in Figure 60.1 in the textbook change when the marble moves from A to C and then from C to B.

lesson 1 page 157 textbook and ly 9

The answer:

At A: The potential energy of the largest marble is equal to WtA; kinetic energy is 0

At C: Zero potential energy and maximum kinetic energy

→ From A to C: The potential energy of the marble decreases; momentum increases.

At B: The potential energy of the marble is equal to WtB and the kinetic energy is zero

→ From C to B: The kinetic energy decreases; potential energy increases.

Lesson C2 (page 157 Physics Textbook 9)

Compare the initial potential energy we distribute to the marble at position A and the potential energy the marble has at point B.

The answer:

The height h1 of the marble A is higher than the height h2 of the marble at B .

→ The potential energy of the marble at A is greater than the potential energy of the marble at B.

Lesson C3 (page 157 Physics Textbook 9)

Can the above test device make the marble have more energy than the potential energy we initially distributed to it? During the movement of the marble, is there any new form of energy besides mechanical energy?

The answer:

The marble cannot have more energy than the potential energy we initially distributed to it. In addition to mechanical energy, there is also thermal energy due to friction of the ball with the floor, causing the ball to heat up.

Lesson C4 (page 158 of Physics Textbook 9)

Let’s show in the experiment in Figure 60.2 Textbook, from which form to which form the energy was converted through each department.

lesson 4 page 158 sgk and ly 9

The answer:

+ From the potential energy of the weight at A changes to its kinetic energy when A moves from A to A’. The kinetic energy of the weight is converted into electricity by the generator.

+ From the electrical energy of the generator to the mechanical energy of the electric motor.

+ From the mechanical energy of the electric motor to the kinetic energy of the ball at B.

+ From the ball’s kinetic energy at B to its potential energy at B’.

Lesson C5 (page 158 of Physics Textbook 9)

Compare the initial potential energy distributed to mass A and the potential energy gained by mass B when it reaches its highest position. Why is there this loss of potential energy?

The answer:

+ Initially, we see that h1 > h2, so the initial potential energy of mass A is greater than the potential energy obtained by mass B.

+ When mass A falls, only part of the potential energy turns into heat, and a part turns into kinetic energy of the weight itself. When the electric current causes the electric motor to rotate and pull the weight B up, only part of the electrical energy is converted into mechanical energy, and part of the electrical energy is converted into heat energy to heat the wire. Due to these losses, the potential energy obtained by mass B is less than the initial potential energy of mass A.

Lesson C6 (page 158 of Physics Textbook 9)

Explain why a perpetual motion machine cannot be built.

The answer:

It is not possible to build a perpetual motor because it is contrary to the law of conservation of energy (energy cannot be created or lost by itself, but only converted from one form to another or transferred from one object to another).

If an engine works, it has potential. This ability cannot be generated by itself. To have this ability, it is necessary to distribute to the machine an initial energy (using the energy of water or burning coal, firewood, oil, …).

Lesson C7 (page 158 of Physics Textbook 9)

On Figure 60.3 the textbook shows an improved wood-burning stove. Please explain why using this type of stove saves fuel rather than using a tripod in Figure 60.4 Textbook.

lesson 7 page 158 sgk and ly 9 lesson 7 page 158 sgk and ly 9 1

The answer:

Heat energy is distributed by firewood, a part of it heats the water, the rest is transferred to the surrounding environment according to the law of conservation of energy. The improved stove has an insulated wall, keeping the heat from being transferred out, making use of the heat to boil two pots of water.

Physics Quiz 9 Lesson 60 with answers

Lesson 1: In natural phenomena, there is often a variation between:

A. Electric and potential energy

B. Potential and kinetic energy

C. Light and kinetic energy

D. Chemical energy and electricity

The answer

In natural phenomena, there is often a change between potential and kinetic energy

Answer: REMOVE

Lesson 2: In the process of converting potential energy into kinetic energy and vice versa in natural phenomena. The mechanical energy is always reduced, the lost mechanical energy has been converted to:

A. Thermal energy

B. Chemical energy

C. Light energy

D. Nuclear energy

The answer

In natural phenomena, there is often a change between potential and kinetic energy.

The potential is always decreasing. The lost mechanical energy is converted into heat.

Answer: A

Lesson 3: In an electric motor, most of the electrical energy is converted into:

A. Electricity

B. Chemical energy

C. Light energy

D. Mechanical energy

The answer

In an electric motor, most of the electrical energy is converted into mechanical energy

Answer: EASY

Exercise 4: Choose the correct statement.

A. In an electric motor, most of the electrical energy is converted into heat.

B. In generators, most of the mechanical energy is converted into chemical energy.

C. The final part of the useful energy is always larger than the initial energy distributed to the machine.

D. The lost energy is converted into another form of energy.

The answer

A – false because: In an electric motor, most of the electrical energy is converted into mechanical energy

B – false because: In generators, most mechanical energy is converted into electrical energy

C – false because: The final part of useful energy is always smaller than the initial energy distributed to the machine.

D – right

The answer to choose is: EASY

Exercise 5: Which of the following statements is true regarding the law of conservation of energy?

A. Energy can be self-generated or destroyed and transferred from one form to another or transferred from one object to another.

B. Energy is not created and destroyed by itself, but can be transferred from one object to another

C. Energy is not created or destroyed by itself, but only converted from one form to another or transferred from one object to another.

D. Energy is neither created nor destroyed, but only converted from one form to another

The answer

Principle of conservation of energy:

Energy is neither created nor destroyed, but only converted from one form to another or transferred from one object to another

Answer:

Lesson 6: In a generator, the generated electrical energy is always smaller than the mechanical energy distributed to the machine. Why?

A. Since a unit of electrical energy is greater than a unit of mechanical energy

B. Because some of the mechanical energy has been converted into a form of energy other than electricity

C. Because a part of the mechanical energy has disappeared by itself

D. Because power quality is higher than mechanical power quality

The answer

In a generator, the generated electrical energy is always smaller than the mechanical energy distributed to the machine, because part of the mechanical energy has been converted into a form of energy other than electrical energy.

Answer: REMOVE

Lesson 7: In the transitions from kinetic energy to potential energy and vice versa, what always happens to mechanical energy?

A. Always be protected

B. Always increasing

C. Always at a loss

D. Sometimes it increases, sometimes it decreases

The answer

In the process of converting kinetic energy to potential energy and vice versa, mechanical energy is always lost. Only when the loss of energy to other forms of energy is neglected is mechanical energy conserved.

Answer:

Lesson 8: Solar cell efficiency is 10%. This means: If the battery receives:

A. If the power is 100J, it will produce 10J . of light

B. Solar energy of 100J will generate electricity of 10J

C. If the power is 10J, it will produce 100J of light

D. Solar energy is 10J, it will generate electricity of 100J

The answer

We have:

+ Solar cells work under the conversion from solar energy to electricity

+ Solar cell efficiency is 10%, that is, if the battery receives 100J of solar energy, it will generate 10J of electricity.

Answer: REMOVE

Lesson 9: Say the electric motor efficiency is 97%. This means that 97% of the electricity used is converted into:

A. mechanical energy

B. thermal energy

C. mechanical and thermal energy

D. mechanical and other energy

The answer

We have, in an electric motor, most of the electrical energy is converted into mechanical energy.

Say electric motor efficiency is 97%. This means that 97% of the used electricity is converted into mechanical energy.

Answer: A

Question 10: Which of the following phenomena does not obey the law of conservation of energy?

A. The stove cools down when the fire is turned off

B. The car stops when the engine is turned off

C. The iron cools down when the power is turned off

D. No phenomenon

The answer

We have:

Principle of conservation of energy:

Energy is neither created nor destroyed, but only converted from one form to another or transferred from one object to another

In all of the above phenomena, there is a conversion of energy from one form to another, and when the loss of energy is neglected into other forms of energy, mechanical energy is conserved.

=> There is no phenomenon that does not obey the law of conservation of energy

Answer: EASY

******************

Above is the content of Physics lesson 9 Lesson 60: Law of conservation of energy prepared by Le Hong Phong High School, including theory, exercise solutions and multiple-choice questions with full answers. We hope that you will master the knowledge of the Law of Conservation of Energy. Wish you all the best in your studies and always get high scores in class tests.

Written by: Le Hong Phong High School

Category: Physics 9

Copyright of the article belongs to High SchoolSoc Trang.Edu.Vn. Any copying is fraud!

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