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When the fraction is 13 / 8, the numerator and denominator subtract a, and the ratio of numerator and denominator is 3:1, what is a?
(13-a)/(8-a)=3/1
3*(8-a)=13-a
24-3a=13-a
2a=11
a=11/2
The denominator of the new simplest fraction is 9 times that of the numerator
Let a number be X
﹙13+X﹚／﹙189+X﹚=1／9
117+9X=189+X
8X=72
X=9
A: a certain number is 9
When a fraction is 17 / 35, and the numerator and denominator are added with the same number, it can be divided into 7 / 13. What is the number added?
Please don't use X to answer
Let the number added be X
Then (17 + x) / (35 + x) = 7 / 13
The solution is x = 4,
So the number added is four
After giving the numerator of 9 / 17 the same number as the denominator, what is the number of 3 / 4 plus
Analysis: the difference between the numerator and denominator of 9 / 17 is 17-9 = 8. The difference between the numerator and denominator of 9 / 17 is still 8. The denominator of the new fraction is 4 and the numerator is 3
Add 9 / 17 to the numerator and denominator of 9 / 17, and you will get 3 / 4. What's the number? Can we not use the equation
Train test
(17-9)/(4-3)=8
3x8-9 = 15 or 4x8-17 = 15
The number is 15
Under what circumstances can holistic method and isolation method be used
Especially for the integral method, if the motion state of two objects is different, can we use the integral method?
The isolation method is to separate the objects to be studied in the connecting body, analyze their forces separately, list their equations, and then solve them simultaneously; the holistic method is to treat several connected objects as a unified whole, and then analyze and solve the whole. Generally, the holistic method and the isolation method should be used together, but it is easier to use the holistic method when the acceleration is involved, The isolation method must be used when the forces between parts of the analysis system are involved
How to use the whole method and the isolation method
Who can tell us in detail how to use, the best with examples, especially the kind of spring
It's hard to make this clear all at once, but to sum it up, there's a sentence:
If the force is the force between two objects (internal force of the system), the isolation method must be used. Generally, the object with less force is selected for detailed analysis;
If the force sought is the force between two objects and the outside world (the external force of the system), then the integral method can be used, and the interaction between the objects and the inside can be ignored
If you can attach some examples, I can give you further analysis and summary
How does the pulley change the direction of the force and save effort
About changing direction: a rope has a mechanical property, that is, it can provide traction along the direction of the rope. So when the direction of the rope is changed by the pulley, the direction of the force changes~
On labor saving: w = FS, do you understand? To do a thing, the work will not change, no matter what way. The pulley can make the distance s increase, so when the work W is constant, f will naturally be small
Use a movable pulley to pull an object weighing 1000 n horizontally at a constant speed. The friction between the object and the ground is 300 n,
The horizontal pulling force F acting on the end of the rope is 250 n, which makes the object advance 10 m. try to find: 1. The effective work and total work of the pulling force 2. The mechanical efficiency of the moving pulley
The horizontal pulling force F acting on the end of the rope is 250 n, which makes the object advance 10 m. try to find: 1. The effective work and total work of the pulling force 2. The mechanical efficiency of the moving pulley
1. Useful work refers to the work done at least when the pulley is not used. In this case, the pulling force is equal to the friction force
W=FS＝300×10＝3000J
The total work is the work done with the moving pulley
W'=F'S',S'=2S=20m
=250×20
=5000J
2. Mechanical efficiency:
η = w yes / W total
＝3000/5000
＝60％
Are the forces on both sides of the pulley the same and opposite?
The same
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