Physics problems of movement and rest in the first to third years of junior high school

According to the direction of the flag and smoke on the car, it is judged that the red car is moving eastward and the speed is greater than the wind speed; There are three situations for a black car, either stationary or moving westward, or moving eastward but at a speed less than the wind.

The wind direction is from west to east, the black car does not move or goes west or goes east at a speed less than the wind speed, and the red car goes east and the speed is greater than the wind speed.

This question can't be a certain remark about the red car, and if I'm not mistaken, it's a multiple-choice question, and there is only one answer after the exclusion.

The wind is westerly, from west to east.

The black car is stationary, or it is driving from east to west.

The red car travels from west to east.

There are three situations of black cars: 1. Stationary; 2. Movement from east to west; From west to east at a speed less than the wind. The red car travels from west to east and is traveling faster than the wind.

The red car moves eastward.

The black trolley moves westward or stationary or eastward at a speed less than the speed of the wind.

The wind is westerly, and there is only one possibility for the red car: it must be moving eastward at a speed greater than the speed of the wind;

There are 3 possibilities for a black car: it may be stationary, it may move west at any speed, or it may move east at a speed less than the speed of the wind.

What is the problem, landlord?

Wind direction to the east; The red car travels eastwards at a speed greater than the wind speed; The black car is heading west, the speed is less than the wind speed, or the black car is stationary.

Taking the position of A at a certain time as the origin, the positive direction of the x-axis to the west and the positive direction of the y-axis to the south, then:

At time t, the coordinates of A are (,0), and the coordinates of B are (0,,,The distance of A and B is h=v[(>=v256=16(m), and when, that is, t=8(s), the minimum distance h of A and B is 16m.

After 12 s their distance is the smallest, and the minimum distance is

Isn't there a lack of conditions for this topic?

The motion and rest of an object are relative.

1) If two objects, A and B, have the same velocity (v A=v B) and the same direction, then the two objects are relatively stationary, that is, object A is stationary relative to object B, and the velocity is 0; Object B is also at rest with respect to object A with a velocity of 0;

2) Objects A and B are at different velocity and in the same direction. If v A >> v B, and the direction of motion is to the right, then object A is moving relative to object B, the speed of motion is v A-v B, and the direction of motion is to the right; The object B is also moving relative to object A, the speed of motion is v A-v B, and the direction of motion is to the left;

3) The velocity of the two objects A and B are respectively (v A, v B) and reversed. If the direction of motion of A is to the right and the direction of motion of B is to the left, then object A is moving relative to object B, the speed of motion is v A + v B, and the direction of motion is right; The object B is also moving relative to object A, the speed of motion is v A-v B, and the direction of motion is to the left;

Quite simply, if you and your friend walk together in the same direction at the same speed, then you are stationary relative to him or him relative to you; On the contrary, you or he is in motion relative to the ground.

If A and B move at the same speed in the same direction at a constant speed. Then A is at rest with respect to B, and likewise, B is at rest with respect to A. However, if we take the ground as a reference, both objects A and B are in motion.

Sports yachts.

3.With a pencil, wrap the copper wire tightly around the pencil n turns, and then use a scale to measure the length of the copper wire wound n turns, divided by the number of turns, that is, the diameter of the copper wire.

The movement becomes smaller.

8.Use a micrometer to measure the diameter of the coin d, l=:1

1a 2 shore boat 3 (whatever you want) 4 22 5d 6 small 7 8 vernier caliper (step omitted) 9 6:1

1. B2, Sports, Yacht.

3. Wrap the thin copper wire tightly around the pencil ten times, and then measure the length of the ten circles, just divide by ten.

km 250km h = 5, d6, decrease of motion.

Wrap the coin around the coin with a string and measure it with a ruler when the rope is straightened.

1、a；

2、d；3、c；

4、b；5、a；

6、c；7、a 。

Question 1: The reason why conductors conduct electricity is because a;

Question 3: AB and BC are connected in series, and the series current is equal everywhere;

Clause. Questions 4 and 5:

The longer the conductor and the smaller the cross-sectional area, the greater the resistance, and under the same conditions, the resistance of the nickel-chromium alloy wire is greater than that of the aluminum wire;

Question 6: The safety voltage should be below 36V;

Question 7: In a circuit, an ammeter is equivalent to a wire, and a voltmeter is equivalent to an open circuit.

R1 and R2 are connected in parallel, A can only be an ammeter, and both meters must have an indication, then B is an ammeter.

The torpedo and the carrier are traveling face to face, and the time the carrier travels at the time of the hit is equal to the time it takes for the torpedo to advance, so t mine = t ship = t

The submarine is far from the aircraft carrier S0, and both the torpedo and the aircraft carrier have traveled T time, and the sum of their distances is, of course, S0, so S mine + S ship = S0

According to s=vt, v mine t+v ship t=s0 gets v mine t + v ship t=s0

Just draw a picture, the fish movement distance after the fish is launched + the aircraft carrier movement distance = the original distance of 5km