Junior physics all derived formula! Thank you!

Junior physics all derived formula! Thank you!

Mechanics: lever balance formula & nbsp; power x power arm = resistance x resistance arm & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; work w = FS & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; power P = w / T & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; & nbsp; efficiency η = w useful

It is the calculation formula of a certain quantity under what conditions in the process of calculating the mechanical efficiency of inclined plane

Calculation of mechanical efficiency of inclined plane:
If we know the height h, the length s of the inclined plane and the pulling force F, then:
η = w / W total = GH / Fs
This is the most commonly used formula
If we know the friction F:
Then: η = Wye / wtotal = Wye / (Wye + Wye), and Wye = FS, that is, the extra work is the work done to overcome friction
The results show that: η = GH / (GH + FS)
Generally speaking, in these two cases, the calculation of inclined plane is relatively simple

How is I1 / I2 = R2 / R1 derived?
I (capital I) is the current and R is the resistance

In parallel circuit, the voltage of each branch is equal
From I = u / R
U1 = i1r2, U2 = i2r2
That is, i1r1 = i2r2
So I1 / I2 = R2 / R1
For reference only! Ask again if you have any questions!

How to deduce the pressure formula of physical liquid in the third year of junior high school?
How is p = ρ GH derived?

p=F/S=ρgV/S=ρgSh/S=ρgh