R1 nối tiếp (đèn song song mn) Có r1=20 ôm, đèn:20v-100w , mn là 1 dd bằng nhôm có l=5000m s=0,2mm^2
a) tính r đèn, r mn ??
b)u=220v, r biến trở bằng 100v hỏi Pđèn P biến Pr
c) r biến trở = 100 ôm đèn sáng bình thường u=?

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Distance covered = speed x timethe distance traveled going against the stream = distance traveled with the stream.therefore it is the speed and the time that are the variables.as he travels the same distance both ways, speed x time is the same for each way.going upstream his speed is 4 kph; going downstream his speed is 6 kph.therefore we have two simultaneous equations: time upstream x 4 = time downstream x 6time upstream + time downstream = 60 minutestherefore we have the equation: time upstream = 6/10 hour, time downstream therefore = 4/10 hour.distance traveled at 4km/hr in 6/10 hour = 24/10 = 2.4km.check: distance traveled at 6km/hr in 4/10 hour = 24/10 = 2.4km.

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