Physics formula in the second semester of 2010 junior high school The second semester of 2010 Physical formula

Physics formula in the second semester of 2010 junior high school The second semester of 2010 Physical formula

Gravity g = mg
Density ρ = m / V
G = ρ GV (derived formula)
Buoyancy f = g row = m row g = ρ liquid GV row
Pressure P = f / S
Hydraulic P fluid = ρ fluid GH
Lever principle -- f1l1 = f2l2
Pulley -- Fixed: F = g, s = h
Dynamic: F = 2G, s = 2H
Group: F = GN (number of ropes around the pulley), s = NH
Work w = FS
Power P = w / T
Mechanical efficiency η = Wye / wtotal × 100% = GH / Fs (when lifting heavy objects) = g / NF (mechanical efficiency of pulley block)
This is our teacher's summary, complete, give me the score

A negatively charged particle, q = - 2 * 10 ^ - 9C, moves from point a to point B in the electrostatic field. In this process, except for the electric field force, the work done by other forces is 6 * 10 ^ - 5J, and the kinetic energy of the particle increases by 8 * 10 ^ - 5J

Using kinetic energy theorem
Qu + W = kinetic energy increased by 8 * 10 ^ - 5J
-2*10^-9U+6*10^-5J=8*10^-5J
U=-10000V

A negatively charged particle, q = - 2 * 10 ^ - 9C, moves from point a to point B in the electrostatic field. In this process, except for the electric field force, the work done by other forces is 6 * 10 ^ - 5J, and the kinetic energy of the particle increases by 8 * 10 ^ - 5J
2. When the particles with zero initial velocity are accelerated by uniform electric field with voltage of u = 4 * 10 ^ 3V, the velocity of 5 * 10 ^ 3m / S is obtained. The time for particles to pass through the accelerating electric field is t = 1 * 10 ^ - 4S. Without considering the effect of gravity, what is the charge mass ratio of the particles? What is the factory strength of uniform electric field? What is the displacement of particles in the process of passing through the electric field?

Q=UIt=15×4×10=3600J

CCTV's "focus interview" column has repeatedly reported that the rural electricity price is too high. The reason for the high electricity price is that the power grid is old and aging, and the power loss is serious. In order to reduce the loss, the following measures are feasible ()
I understand other options by myself. But why can't I "shorten the length of the wire"? Does the resistance shrink soon after shortening the length? Does the power loss shrink soon?

Pro, don't just look at theory and ignore practice
If you think about the distance between regions, how can you shrink it