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The object changes speed under the action of external force When an object changes speed under the action of external force, the kinetic energy must change The kinetic energy of an object remains unchanged, and the combined external force must be zero Why are these two sentences wrong?
The first special case is uniform circular motion
Velocity is a vector, so when the velocity direction changes, the velocity also changes, but the kinetic energy does not necessarily change
The second: the same as above. The kinetic energy remains unchanged. It may be a uniform circular motion, and the combined external force is not 0
Put one piece of aluminum and one piece of iron on both sides of the adjusted balance to maintain the balance of Libra, and calculate the volume ratio of aluminum and iron? Help speed```
Volume ratio of aluminum block to iron block = density ratio of iron block to aluminum block
1. Physical quantity of () 2.1m/S=（ ）Km/h 1Om/S=（ ）Km/h 72Km/h=（ ）m/S 1.08Km/h=（ ）m/S 5. When something moves at a uniform speed of 160m, it takes 20 seconds to find the speed of the object
1. How fast does an object move
2、3.6,36,20,0.3
2、Vt＝S,20V＝160,V＝8m╱s
The nameplate of an electric kettle is marked with "220V 1000W". What is the current when he works normally? Come on
Analysis: I = P / u = 1000W / 220V = 4.55a
Don't know, ask me
The resistance value of resistance E1 is 15 ohms and the resistance value of resistance R2 is 10 ohms. The current through resistance R1 is 0.2A. Find (1) the voltage representation and (2) the ammeter representation. The diagram of this problem is in parallel. I found it from the book
R1 and R2 are in parallel, so U1 = U2
And U1 = I1 * R1 = 0.2A * 15 = 3V
Therefore, the voltmeter is 3V
Current through I2 I2 = U2 / r2 = 3 / 10 = 0.3A
If the ammeter measures I2 current, the indication is 0.3A. If the ammeter measures trunk current, the indication is 0.3 + 0.2 = 0.5A
In winter, there is a layer of frost on the car window, which is formed in_____ (choose "outside the window", "inside the window"). In order to eliminate it as soon as possible, the car should be opened at this time____ (select "hot air" and "cold air")
Analysis: the frost is formed by the condensation of hot water vapor in the car when it is cooled, so it is formed in the window
At this time, cold air should be turned on to cool the hot water vapor,
Conclusion: there is no cold air in the window
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