A train runs at a constant speed on a flat track, and a passenger drops two objects a and B from the window. If the air resistance is negligible, what will happen when they fall freely () A. A is directly below B B. A is directly behind B C. A is under the front of B D. A is under the back of B I want a solution But I lost it in different order.

If there is no air resistance, then a, B and train speed are the same
So a is right below B
So a is not at the same level as B, but below
They are moving at the same speed as trains, or people, but they are outside people's windows

1. When Xiao Ming looks out of the window in the car, the number he sees at 12:00 is a two digit number, and the sum of the numbers is 7; the number he sees at 13:00 is just the opposite of the previous one, and the number he sees at 14:00 is a three digit number, which is one more 0 than the number he sees at 12:00, so the number he sees at 12:00? (the car runs at a constant speed)
2. Party A and Party B are going from a and B at the same time. The first time they meet is 700 meters away from A. then they continue to move forward and return immediately after arriving. The second time they meet is 400 meters away from B. what is the distance between a and B?
3. If someone rides a bicycle from home to the railway station, if he travels 30 kilometers per hour, he can arrive 15 minutes earlier. If he travels 18 kilometers per hour, he will be 15 minutes late. If he wants to arrive 10 minutes earlier, what speed should he drive?
4. After breaking up, Party A and Party B went in the opposite direction along the railway track. At this time, a train came to Party A at a constant speed. It took 15 seconds for the train to pass by Party A, and then it took 17 seconds for the train to pass by Party B. It is known that the walking speed of both of them is 3.6 km / h. how about the speed and length of the train?
5. At 8:00 a.m., Xiao Ming went to the countryside to climb a mountain. The walking speed was 10 km / h, and the driving speed was three times of the walking speed. He walked half the way and took half the car. After playing for four hours, he returned. When he returned, he took half the time to go by car and half the time to walk. As a result, it took 40 minutes less to return than when he went?

The answer is 16
You have two ways to do it. 1) try algebra directly and substitute 3 & 41 & 62 & 5 to verify it
2) Of course, if it's solving a problem, you can set the value directly. At 12:00, you will see AB (a, B only represents numerical value)
13:00 ba 14:00 a0b
Then a + B = 7, uniform driving distance is the same, then (b * 10 + a) - (a * 10 + b) = (a * 100 + b) - (b * 10 + a)
The two equations solve that a and B are 1 and 6
I hope I can help

When Xiao Ming took the train and looked out of the window for the first time, he happened to see that the number of kilometers on the roadside milestone was double digits of 6. He wrapped it for 0 minutes and then went back to work
When I looked out of the car, I saw that the kilometer on the road milestone was just the original two digit number, and the front and back positions were exchanged. After another 20 minutes, I looked out of the window and saw that the kilometer on the road milestone was three digits, and it was just the middle of the two digit number that I saw for the first time, which was one more 0

If you think about the unknown number, it should be 1, but I still give you the process: let's set the unknown number as X, then 60 + x-10x-6 = 100x + 6-60-x, once a dollar is not difficult to solve, x = 1. I won't explain this equation. If you know that the unknown number is 1, then the first mileage is 16, the second is 61, and the third is 106. Then you can drive 45 kilometers every 20 minutes, The train speed should be 135 km / h

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