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When a train leaves from the station, it accelerates uniformly and moves in a straight line. When it starts, the operator on duty stands beside the front end of the first carriage. It takes 4 seconds for the first carriage to pass by him, and 20 seconds for the whole train to pass by him. The length of each carriage is equal, and the length of the carriage joint is not included. How many carriages are there in this train? How long does it take for the last nine carriages to pass by him
The average speed of the first and all cars should be proportional to the passing time
So the average speed ratio is 1:5
There are n cars in each length s
If 5 * s / 4 = n * s / 20, n = 25
Because s = 1 / 2 * a * T ^ 2
So start at rest
The square of time is proportional to the displacement
16 / 25 = t * 2 / 400 t = 8 * radical 5
So the experience time is 20-8 * root 5
When a train departs from the station to make a uniform acceleration linear motion, the attendant stands in the first section
A train starts from the station and accelerates in a straight line. When it starts, the operator on duty stands beside the front end of the first carriage
It takes 4 seconds for the first carriage to pass him, and 20 seconds for the whole train to pass him. Suppose that each carriage is equal in length, and the length of the joint of the carriages is not taken into account. How many carriages does this train have? (2) how long does it take for the last carriage to pass him?
S=1/2Xat^2
Length of each car = 1 / 2xax16 = 8A
Total car length = 1 / 2xax400 = 200A
Number of cars = 200 / 8 = 25
24x8a = 1 / 2xat ^ 2
t=19.596s
When the last car passed him: T = 20-19.596 = 0.4s
A small screw fell off the ceiling of a train speeding up evenly. What's the movement of the screw when people on the train see it?
What you're talking about is constant acceleration. The speed of the small screw in the horizontal direction is the train speed at the moment when it falls down, and you will increase with the train speed, so the speed difference between the small screw and you is also increasing. The speed of the screw in the vertical direction is also increasing. On the whole, its trajectory should be an inclined straight line. In the horizontal direction, you can understand it as inertial acceleration, The vertical direction can be understood as the acceleration of gravity. The acceleration of the two directions is constant and can be synthesized, that is, to make a uniform acceleration linear motion
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