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Let's teach me the concept of electric power I don't know why w = I ^ 2rt and w = u ^ 2T / R must be used in pure resistance circuit? ||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||||
Let's make clear a few nouns
Electric work: the size of the current attack, the definition: w = u * I * t
Electric power: the speed of electric work, definition: P = u * I
Ohm's Law: when current flows through pure resistance, the relationship among current I, resistance R and voltage U is: I = u / R. in other words, current flows through pure resistance and is only used to generate heat!
In other words, when the research object is pure resistance, u is replaced by I * r
W＝U*I*t＝（I*R)*I*t＝I^2*R*t
Or I use U / R instead
W＝U*I*t＝U*（U/R)*t＝U^2/R*t
Physics problem (need necessary explanation)
Xiaojie's speed is 20km / h for the first half of the journey and 10km / h for the second half
Let the distance be L
The first half time T1 = (L / 2) / 20 = L / 40
The second half time T2 = (L / 2) / 10 = L / 20
Ttotal = T1 + T2 = 3L / 40
V = L / T total = 40 / 3 km / h
Understand, to the necessary text, formula and calculation steps
Let me just describe it in the figure. There are two pulleys at the top and bottom, four in total. Use it to lift materials. (1) use 100N vertical upward tension to lift 300N objects at a uniform speed, and calculate the mechanical efficiency of the pulley block. (2) use this pulley block to make 600N objects rise 2m at a uniform speed in four seconds, Calculate the work and power of the worker in these four seconds
It's the pulley block. There are two on the top and two on the bottom. The pulling force is upward, so there are five strands of rope!
1. If the number of ropes on the moving pulley is n = 5, then η = w you / W total = g / NF = G1 / 5F = 300N / 500N = 60% 2. G dynamic = nf-g1 = 500n-300n = 200nw you = GH = 600N × 2m = 1200jw total = (G + G dynamic) H = (600N + 200N) × 2m = 1600jp = w / T = 1600j / 4S = 400W
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