Physics 8 Lesson 18: Questions and exercises to summarize chapter I Mechanics
1. Theoretical summary
1.1. Review questions
1. What is mechanical movement? Give 2 examples.

It is the change in position over time of one object relative to another.

Example: Walk, ride a bike.
2. Give an example that shows that an object can move relative to one object but remain at rest relative to another?
When a passenger is sitting in a moving car, the passenger moves with respect to the roadside tree, but is stationary relative to the car.
3. The magnitude of velocity characterizes what property of motion? Speed calculation formula? Velocity unit?
4. What is irregular motion? Write a formula for the average velocity of a nonuniform motion.

Irregular motion is motion in which the magnitude of the velocity changes with time.

Formula for average velocity: \(v_{{tb}}=\frac{s}{t}\)
5. What effect does force have on velocity? Mentioned examples.

A force that changes the velocity of an object.

For example: The attraction of a magnet on a piece of steel increases the speed of the wheelchair, so the wheelchair moves faster.
6. What are the factors of force and how to represent force?
– Elements of force: set point, direction, direction and magnitude.
– How to show force:

The origin is the point at which the force acts on the object (called the point of application of the force).

Direction and direction are the direction and direction of the force.

Length represents the magnitude (magnitude) of the force on a given scale.
7. What are two balancing forces?
Balanced forces are two forces that are applied to an object, have equal magnitude, lie on the same line, opposite directions.
8. When does the force of friction appear? Give two examples of frictional forces.
Friction occurs when an object slides, rolls, or rests on the surface of another object.
Eg:
9. Give two examples to show that an object has inertia.

When the car suddenly turns right, the passengers in the car are tilted to the left.

When jumping from a high step, our legs are bent.
10. On what factors does the effect of pressure depend? Pressure formula. Pressure unit.

The effect of pressure depends on two factors: The magnitude of the force acting on the object and the surface area in contact with the object.

Formula for pressure: \(p=\frac{F}{S}\)

The unit of pressure is paxcan: 1Pa = 1 N/m^{2}.
11. An object immersed in a liquid is acted upon by a force of magnitude, direction, and direction?

Thrust has a vertical direction, from the bottom up, and is equal to the weight of the liquid displaced by the object.

This force is called the Archimedes repulsion.
12. Conditions for an object to sink, float, or suspend in a liquid.
– Sink down : P > F_{A}
– Emerging : P < F_{A}
– Floating : P = F_{A}
In there :
13. In what case is the term mechanical work only used in science?
In science, the term mechanical work is used only in the case of a force acting on an object that causes the object to move.
14. Write the expression for mechanical work. Clearly explain each quantity in the work expression. Public unit.
– The expression for mechanical work: A = Fs
In there:

F: force acting on the object (N).

s: distance traveled in the direction of force (m).

The unit of work is the joule, symbol J (1J = 1 Nm).
Note: The symbol for Kilojun is (kJ) (1 kJ = 1000 J).
15. State the law of public.

There is no simple machine that gives us any advantage in work.

How many times you gain in terms of force, how many times do you lose on the way and vice versa.
16. What does power tell us?
Power tells us the ability of a person or a machine to do work in a unit of time.
17. What is conservation of mechanical energy? Give three examples of conversion from one form of mechanical energy to another.
In a mechanical process, kinetic and potential energy can be converted to each other, but mechanical energy is conserved.
Eg:

Arrows are fired from the bow.

Water flows down from the high dam.

Throw an object vertically upwards.
1.2. Application question
Lesson 1: Two forces are said to be in equilibrium when:
A. Same direction, same direction, same magnitude.
B. Same direction, opposite direction, same magnitude.
C. Same direction, opposite direction, same magnitude.
D. Same direction, same magnitude, placed on the same object.
Placed on the same object, the same magnitude, the direction lies on the same line, opposite directions.
⇒ Choose answer D.
Lesson 2: The moving car suddenly stopped. Passengers in the vehicle are:
A. Lean back.
B. Lean to the left.
C. Lean to the right.
D. Push people forward.
Push people forward.
⇒ Choose answer D.
Lesson 3: A convoy of motorcycles moving in the same direction, with the same speed, passed a car parked on the side of the road. Which of the following comments is correct?
A. Motorcycles move relative to each other.
B. The motorcycles are at rest with respect to each other.
C. Motorcycles are stationary with respect to cars.
D. Motorcycles and cars move together with respect to the road surface.
The motorcycles are at rest with respect to each other.
⇒ Choose answer B.
2. Illustrated exercise
2.1. Form 1: Find the pressure a person acts on the ground
A person has a mass of 45 kg. The ground contact area of each foot is 150 cm^{2}. Calculate the pressure the person exerts on the ground when:
a) Stand with both feet.
b) Bend one leg.
Solution guide
The weight of the person is: P = 45.10 = 450 N.
a) When standing with both feet, the area in contact with the ground is:
S = 150.2 = 300 cm^{2} = 0.03 m^{2}
The pressure when standing with both feet is:
\(p = \frac{P}{S} = \frac{{450}}{{0,03}} = 15000N/{m^2}\)
b) When one leg is bent, the contact area is halved:
S_{first} = S/2 = 150 cm^{2} = 0.015 m^{2}
The pressure when standing on one leg is:
\(p = \frac{P}{{{S_1}}} = \frac{{450}}{{0,015}} = 30000N/{m^2}\)
2.2. Form 2: Determination of work done
Calculate the work you can do, when going from the first floor to the second floor of your school (you give the necessary data yourself).
Solution guide
 Suppose your mass is 40 kg, then the weight is 400N; The height from 1st floor to 2nd floor is 5m.
 When walking steadily from the 1st floor to the 2nd floor, the lifting force F = P.
⇒ Work done: A = Fh = 400.5 = 2000J.
3. Practice
3.1. Essay exercises
Question 1: The motion of the pendulum when going from the equilibrium position (with an angle α = 0 with the vertical)^{o}) out the boundary position (with the largest angle α with the vertical) is the motion with what speed?
Verse 2: The atmosphere around the Earth is about 160 km thick. Gravity keeps them from escaping into space. How does that layer of gas affect us when climbing high mountains?
Question 3: An object with mass 3600 g has a density of 1.8 g/cm^{3}. When dropped into a liquid with a specific gravity of 8500 N/m^{3}, it is completely below the surface of the liquid. What is the magnitude of the force that pushes the Archimede on the object?
Question 4: A person stands with two thin boards placed on the floor and exerts a pressure of 1.6.104 N/m on the floor.^{2}. The area of a plank in contact with the floor is 2dm .^{2}. Neglecting the mass of the board, what is the corresponding mass of the person?
3.2. Multiple choice exercises
Question 1: A car moves in a straight line along the road from point M to point N with an estimated time t. If the car’s speed is increased by 1.5 times, the time
A. 2/3 times decrease B. 4/3 times increase
C. reduced by 3/4 times D. increased by 3/2 times
Verse 2: A passenger car is moving along a 54 km road with a speed of 36 km/h. The time taken by the car to travel that distance is:
A. 2/3 hours B. 1.5 hours C. 75 minutes D. 120 minutes
Question 3: Which of the following does mechanical work?
A. A heavy object falls from a height.
B. Current flows through the resistance wire to heat the electric stove.
C. The Moon revolves around the Earth under the influence of gravity.
D. Water is boiled by gas stove.
Question 4: Our hands can grasp objects thanks to:
A. sliding friction B. resting friction
C. rolling friction D. inertia
4. Conclusion
Through this lecture summarizing chapter I Mechanics, you need to complete some of the objectives given by the lesson, such as:

System is knowledge of chapter Mechanics

Answer the review questions. Do well the exercises in the application section.
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