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There is an observer on the platform of the railway station. When the train starts, it just stands at the front end of the first carriage. After the train starts, it makes uniform acceleration and linear movement. At the end of 5S, the end of the first carriage passes through the observer (each carriage is the same length). Then: (1) Observe the passage from the beginning______ Seconds, the end of the 9th carriage passes through the observer; (2) The time for the 9th carriage to pass through the observer is______ Seconds
When the end of the first carriage passes through the observer: X1 = 1
2at12，
When the end of the 9th carriage passes through the observer: x9 = 1
2at92：
x9=9x1
So T9 = 3t1 = 15s
When the end of the 8th carriage passes through the observer: X8 = 1
2at82
x8=8x1
So T8 = 10
2s
△t＝t9−t8＝15−10
2s
So the answer is: 15; 15−10
two
The train moves in a straight line along the east-west direction. There is a small ball on the smooth horizontal table in the train. When the passengers see the small ball, it suddenly rolls eastward along the table The answer may be that the train () moves at a uniform speed from west to west, and it should move in a straight line with uniform acceleration But why can't we choose to make a uniform linear motion instead of a uniform accelerated linear motion to the east
It can be inferred from the last "when the passenger sees the ball suddenly rolling eastward along the table" that the ball was originally stationary, then the motion state of the train at that time is stationary or uniform motion. Combined with the first sentence "the train moves in a straight line along the east-west direction", it can only be concluded that the train was moving at uniform speed at that time; Now that the ball rolls eastward, it means that the train is moving westward and accelerating or moving eastward and decelerating. Why is the answer you listed? The optional answer is probably in line with it
As for your proposal of "changing the uniform acceleration linear motion from east to uniform velocity linear motion", the passenger sees that the uniform acceleration motion of the small ball to West suddenly becomes uniform motion. It is suggested to review Newton's first and second laws, key words inertia, force and acceleration
In order to study the movement of the maglev train, a classmate put a glass square cup containing water on the horizontal table in the train. As shown in the figure, the side ab of the water surface in the square cup is 8 cm long. At a certain time when the train is moving in a straight line, he found that the speed displayed on the electronic information screen is 72 km / h, and the water surface in the front of the cup has decreased by 0.5cm. This phenomenon has been stable until the speed is 288 km / h, When the water level at the front side starts to rise, what is the displacement of the train in the above stability stage? If the total mass of the train is 3 × 104 kg, resistance f = k V2 (known k = 2 NS2 / m2, V is the speed, unit M / s), try to write the expression of traction force of train motor in the above stable stage with respect to time t ------------------------------------------------------------------ 1. When calculating the acceleration, can you "obviously" a for a reason, because if you look at the diagram, you will intuitively think it is the answer 2. The answer in the following question book is 2400. I calculated that the answer is much larger than this. Am I wrong? I think it should be really big. How can it be more than 2000 The acceleration is 1.25. Why is the displacement 2400?!
From v = 20m / s to 80m / s, the time is 48S. Isn't the displacement 2400m?
When calculating the acceleration, directly analyze the force on a small particle, and then decompose it, almost
It takes about 15 hours for a train to arrive in Guangzhou from Beijing. After the train starts, it will travel at the same speed for 8 hours and then arrive in Wuhan. Since the Wuhan Guangzhou high speed railway, the world's highest speed railway, was officially put into operation in December 2009, the average speed of the train from Wuhan to Guangzhou is more than 50 kilometers per hour, The average speed of the train from Beijing to Wuhan and the average speed of Wuhan to Guangzhou after speed increase are calculated
It is assumed that the average speed of trains from Beijing to Wuhan is x km / h, and the average speed from Wuhan to Guangzhou after speed increase is y km / h
According to the meaning of the title, there are
y＝2x+50
15x＝8x+(15−8−4)y
Solve the equations and obtain
x＝150
y＝350
A: the average train speed from Beijing to Wuhan is 150 kilometers per hour. After the speed increase, the average train speed from Wuhan to Guangzhou is 350 kilometers per hour
It takes about 15 hours for a train to arrive in Guangzhou from Beijing. After the train starts, it will travel at the same speed for 8 hours and then arrive in Wuhan. Since the Wuhan Guangzhou high speed railway, the world's highest speed railway, was officially put into operation in December 2009, the average speed of the train from Wuhan to Guangzhou is more than 50 kilometers per hour, The average speed of the train from Beijing to Wuhan and the average speed of Wuhan to Guangzhou after speed increase are calculated
It is assumed that the average speed of trains from Beijing to Wuhan is x km / h, and the average speed from Wuhan to Guangzhou after speed increase is y km / h
According to the meaning of the title, there are
y＝2x+50
15x＝8x+(15−8−4)y
Solve the equations and obtain
x＝150
y＝350
A: the average train speed from Beijing to Wuhan is 150 kilometers per hour. After the speed increase, the average train speed from Wuhan to Guangzhou is 350 kilometers per hour
It takes about 15 hours for a train to start from Beijing and arrive in Guangzhou. After the train starts, it will travel at the same speed for 8 hours and then arrive in Wuhan. Since the Wuhan Guangzhou high speed railway, the world's fastest railway per hour, was officially put into operation in December 2009, the average speed of the train from Wuhan to Guangzhou is twice that of the original, more than 50 kilometers per hour, and the time required is four hours shorter than the original, Find the average speed from Beijing to Wuhan and the average speed from Wuhan to Guangzhou after the speed increase. Find a complete explanation
Suppose the average speed of the train from Beijing to Wuhan is x km / h, and the average speed from Wuhan to Guangzhou after speed increase is y km / h. from the solution of y = 2x + 50 7x = 3Y, x = 150 y = 350 answer: the average speed of the train from Beijing to Wuhan is 150 km / h, and the average speed from Wuhan to Guangzhou after speed increase is 350 km / h
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