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15. The correct one of the following statements is () A. Light from a light source always travels in a straight line B. The speed of light is always 3 × 108 m/s C. The path of light in the air is straight D. Observe the image formed by the object through the small hole. The closer the eye is to the small hole, the more obvious the observed image is
Choose D because a and C light can become a curve in air. B is 3 × 10 to the 8th square meter per second
Very simple physics problem! Two resistors R1: R2 = 3:5. When two resistors are connected to 6V power supply in series, the ratio of current passing through the two resistors is and the ratio of voltage at both ends of the two resistors is; When two resistors are connected in series to 12V power supply, the current ratio is and the voltage ratio is. (process!) Anyone here?
The series circuit current is the same, so the current ratio is 1:1. The greater the resistance in the series circuit, the greater the voltage. The voltage ratio is equal to the resistance ratio, so the voltage ratio is 3:5
Before boiling, heat the water to the temperature __; When boiling, continue to heat the water, and the temperature of the water is __
Before boiling, heat the water and increase the temperature of the water; When boiling, continue to heat the water, and the temperature of the water remains unchanged
Why do the initial velocities of metal balls of different masses slide freely from the same height on the inclined plane fixed at an angle to the horizontal plane? Can I think so? Because the formula of gravitational potential energy is MGH and the formula of kinetic energy is 1 / 2mv2, then only gravitational potential energy is converted into kinetic energy, that is, MGH = 1 / 2mv2, and M is cut off at the same time, that is, V has nothing to do with m, but has something to do with H and g. is this analysis correct?
yes
These junior high school science questions When an object on a smooth horizontal plane is subjected to two forces of equal magnitude and opposite directions at the same time, the motion state of the object is () When sprinters start, both feet pedal on the starter fixed on the ground. The main function of this is to reduce the angle between the rebound force and the ground?
Moving in a straight line at a constant speed, or at rest
An included angle is formed between the starter and the ground. Because the relationship between the force and the reaction force is the same and the direction is opposite, the closer the man's force on the ground is to the level, the smaller the included angle with the ground, the closer the man's reaction force is to the water level, and the smaller the included angle with the ground, the forward acceleration can be obtained, which is more conducive to starting~~~
Fill in the blanks above is also a hint
Scientific physics in junior middle school (about the density of water) The label of a bottled Baijiu liquor produced by a winery is written in the words "500 milliliters 45 degrees". What is the quality of such a bottle of wine? What is the density of this wine? (alcohol degree refers to the volume of alcohol in 100ml liquor (ML), regardless of the change in volume during blending
M wine= ρ water × 55% × 500+ ρ alcohol × 45% × 500 (here) ρ The unit shall be g / cm ³, M liquor (unit: G, density check table)
ρ Wine = m wine / 500 g / cm ³
RELATED INFORMATIONS
- 1. It will be found when heating the ice water mixture () A the temperature of water increases and the temperature of ice remains unchanged B the temperature of ice rises and the temperature of water remains unchanged C the temperature of water and ice rises together D until all ice becomes water, their temperature remains unchanged
- 2. About the change of state! There is a thermometer with uniform scale but inaccurate number. After test, it is shown as 3 ℃ in the ice water mixture under one standard atmospheric pressure. After it is put into the boiling water under one standard atmospheric pressure, it is shown as 93 ℃ after stabilization (1) . when it displays 12 ℃, what is the actual temperature? (2) When the actual temperature is 50 ℃, what is the reading of this thermometer? (3) What is the reading of this thermometer exactly equal to the actual temperature? Because I want the answer tonight, tomorrow is meaningless, and because I can't wait too long, I'm afraid no one will answer tonight, so I won't give the reward first. But when I choose the correct answer, I will give the reward Mark the question number clearly when answering
- 3. What is the end of mankind and where will mankind eventually go? With the continuous development of society, what will it eventually become?
- 4. Due to the rapid development of science and technology, mankind is using the ocean to develop a new era of the ocean
- 5. Extreme ε-δ Proof of definition Can anyone be specific
- 6. A hexagon can be divided into at least several triangles. How many diagonals can be drawn from one of its vertices? As mentioned in the title
- 7. Triangle has______ One edge______ A corner______ A vertex
- 8. How to draw the vertical line of the opposite side through the three vertices of the triangle
- 9. How to judge whether a sequence has a limit
- 10. 3 mathematical analysis proof questions! (real analysis, sequence, limit) When n approaches infinity, the sequence Sn / N = non-zero constant C. It is proved that the sequence Sn diverges to infinity The real number equation f is uniformly continuous on R. if FN (x) = f (x + 1 / N), it is proved that the sequence FN is always continuous and tends to F Proof: there is no continuous equation G: R - > R, so that G (x) = C has exactly two solutions (C is any real number) The second question should be: verify that the sequence FN is uniformly continuous and tends to F
- 11. There is an environment-friendly flashlight. There is no battery in the flashlight. When in use, as long as the flashlight is shaken back and forth to make the permanent magnet move back and forth through the coil between the two rubber pads in the flashlight, the bulb can emit light. This kind of flashlight can generate electricity______ Principle. The method to increase the brightness of the bulb is______ (just write one)
- 12. Gently put a mass m into a container filled with water, and overflow water with mass m from the container, the floating and sinking of the mass in the water is judged correctly as follows: A. If M > m, the block will sink B. If M > m, the block will float up C. If M = m, the mass must be suspended D. If M = m, the mass may be floating I think the question is wrong. D is right. Please give me some advice M> M must sink, but M = m may float or float
- 13. The electric appliance with a resistance of 40 ohms is connected to a power supply. Through the power of 2C, the work done by the current is 24J. What is the voltage at both ends of the power supply? What is the current through the conductor?
- 14. 1. When a child with a mass of 30kg sits on a 10kg sled, the adult pulls the sled with a pulling force of 100N inclined upward at 37 ° to the horizontal direction to make the sled move at a uniform speed along the horizontal bottom, sin37 ° = 0.6, cos37 ° = 0.8. Find: (1) The pressure of the sled on the ground; (2) The dynamic friction coefficient between sled and horizontal bottom 2. Object a moves in a straight line at a constant speed, with a speed of 2m / s. After a starts for 4S, object B starts from the same place and starts to move in a straight line at a constant acceleration, with an acceleration of 2m / s ², And a and B move in the same direction. Find out (1) how long after B starts to catch up with a (2) the maximum distance before a and B meet 3. There is an object with a mass of 2kg on the horizontal bottom, and the dynamic friction coefficient between it and the bottom is 0.25. Under the action of thrust f inclined downward at 30 ° to the horizontal direction, as shown in the figure, the object makes uniform acceleration from standstill and moves forward 4m within 2S. What is the thrust f? 4. A small block with a mass of M = 2.0kg rushes up the inclined plane with an inclination of 37 ° at a certain initial speed. A student uses a sensor to measure the instantaneous speed of the small block at multiple times in the process of rushing up the inclined plane, and uses a computer to make the V-T diagram line of the sliding process of the small block, as shown in the figure (sin37 = 0.6 cos37 = 0.8 g = 10m / s) ²） Requirements: (1) The acceleration of small blocks when they rush up the inclined plane; (2) Dynamic friction coefficient between small block and inclined plane
- 15. How long does it take for an object to reach the midpoint of a smooth slope? (know that the length of the inclined plane is l, the final speed is V, and the speed at the midpoint of the inclined plane is v / radical 2) We also know that the time that the object passes through the inclined plane is t, please use t to express the answer
- 16. The "sharp and thin" voice of female students refers to the voice of female students______ This is because the vocal cords vibrate more when the female students speak______ For the sake of
- 17. What vibration produces the sound of blowing on an empty bottle
- 18. Knocking on a bottle makes a sound. Is it bottle vibration or water vibration Such as title
- 19. Sound propagates the () of the sound source through the medium in the form of (), which is sound wave
- 20. In the process of sound transmission, the following statement is correct () A. The timbre will gradually change B. The tone will gradually decrease C. The loudness will gradually decrease D. The timbre, pitch and loudness of the sound will not change