Good Samaritans teach physics in the second year of junior high school, and physics in the second ye

If an object can remain at rest or move in a straight line at a uniform speed when it is subjected to two forces, we say that the object is in equilibrium.

Two forces acting on the same object at the same time on the same straight line, if the object remains at rest or in a uniform linear motion, then the effect of these two forces on the motion of the object cancels each other out (the net force is 0), we say that the two forces are balanced.

The gist is:

Size: Equal.

Direction: Opposite (and on the same line).

Two forces act on the same object.

Effect of action: The condition of the equilibrium of the two forces in which the object remains stationary or moves in either direction in a uniform linear motion state is simply homogeneous, equal, reversed, and collinear. In particular, the conditions of "homogeneity" and "collinearity" are often missed by beginners, resulting in incorrect judgments about the balance of the two forces.

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The main points of the balance of two forces: equal in magnitude (equal force), opposite in direction (different directions), acting on the same straight line (two forces should be on the same horizontal line), two forces acting on the same object (gravity, tension, friction).

There is no clear requirement in the balance of forces, which force must be required to cancel the effect, as long as the conditions of the balance force are met.

The speed of light is 300,000 km/s, and the light emitted from Vega is needed to reach Earth.

Convert to adulthood is.

Year. That is to say, we now see that the light of Vega was emitted more than 26 years ago. That's pretty much the way it goes, I don't know if the calculation results are right, you can check it again!

by =m v

Get v=m =......=

v=sl s=4mm 2=4x10 -6 m 2, so l=v s=......=2500m

Because 2500m 2000m

So that's enough!

1.When this resistance wire is connected to the 36V circuit, the current is, indicating that the resistance is 72 ohms, and it can pass through a maximum of 2A current, and it must be in a 220V circuit, so its total voltage should be 110, and it already has a voltage of 38V, so it needs a 38V voltage, which needs to be connected in series.

2. The current is 5A when working normally. , indicating that the rated current is 5A, and its resistance is 16 ohms, indicating that his rated voltage can only be 8V, but it is connected to the lighting circuit. It means that the voltage is 220V at this time, and in order to ensure that it works normally, its resistance should be 44 ohms, and it itself has 16 ohms, so it must be connected in series with a 28 ohm resistor.

It's finally over, it's over. o(oThank you.)

1 r=u i=36 ohms, when the shirt u=220, r=u i=220 2=110, so r=110-52=58 ohms, so a 58 ohm resistor should be connected in series.

2 r=u i=220 5=44 so r=44-16=28, so a 28 ohm electric lift finch cavity resistance is connected in series.

1.Connect a 38 ohm resistor in series. 2.A 28 ohm resistor is connected in series.

Connect a 38 ohm resistor in series.

(1) 50n (2) 10n (3) 6n (4) The resultant force is: horizontal forward direction, size 3N wooden block accelerates forward movement.

Let the masses of both metals be equal to 1 (1 unit, which can also be expressed by m), then the volume of the two is (1 rou1)+(1 rou2), and the total mass of the two is 2, so the density of the alloy is 2 = 2(rou1*rou2) (rou1+rou2).

Equal volume (both set to 1), then the mass is rou1+rou2, and the total volume is 2, so the density is (rou1+rou2) 2

The key to this problem is to set a mass, and to solve the density, remember that it is the mass divided by the volume.

The air quality inside an empty bottle can be determined using the isovolumetric method.

1. Determine the mass of the empty inkwell m0

2. Measure the mass m1 of the inkwell filled with water

Then the volume of the inkwell is the volume of water v=(m1-m0) p water, then the air quality inside the inkwell is p air*(m1-m0) p water.

Solution: (1) Use a balance to measure the mass of the empty ink bottle, which is recorded as m1;

2) Fill the inkwell with water, measure the total mass of the inkwell and the water, and record it as m2;

3) Calculate the volume of water in the inkwell, denoted as v; v = (m2-m1) p water (4) calculates the mass of the air in the inkwell, denoted as empty v = p empty (m2-m1) p water.

The empty inkwell is filled with water, its weight is measured with a balance, and then the weight of the empty inkwell is measured, and the mass of the water is obtained by subtracting, and the density of the water is 1000kg m3, according to.

v = m p to calculate the volume v of the empty inkwell, and then the air quality m = pv from the known air density

1.Fill the bottle with water. Weigh;

2.Pour out the water, weigh;

3.Water and air occupy the same volume, and the equation is used to find the air quality.

Question 3? Solution: Let the distance between A and the cliff be x.

x+(x-20m s*10)] divided by 340m s=10

Solution, x=1800m

Related, different substances reflect sound to different degrees

(1) No, light travels faster than sound.

2）x=340m/sx5s=1700m