Question

a boat, whose speed in still water is 20 km/h, travels 36 km upstream in 2hrs.

a. Find the speed of the stream
b. If the boat travels 36 km downstream, find it's average speed for the whole journey

sebuah perahu yang kecepatannya di air tenang 20 km/jam menempuh jarak 36 km ke hulu dalam waktu 2 jam.

a. Tentukan kecepatan aliran
b. Jika perahu menempuh jarak 36 km ke hilir, tentukan kecepatan rata-rata untuk seluruh perjalanan

sertakan caranya (include how), tolong cepat ya mau dikumpulkan besok​

Answer 1

Jawaban:

a. If a boat whose speed in still water is 20 km/h, travels 36 km upstream in 2 hours, we can use the following formula to find the speed of the stream (let the speed of the stream be s):

speed in still water - speed of stream = speed upstream

20 - s = 36/2

20 - s = 18

s = 2 km/h

Therefore, the speed of the stream is 2 km/h.

b. To find the average speed for the whole journey when the boat travels 36 km downstream, we can use the formula:

average speed = total distance / total time

Let the speed of the stream be s, and the distance downstream be x. Then, the distance upstream is also x.

speed downstream = speed in still water + speed of stream = 20 + s

speed upstream = speed in still water - speed of stream = 20 - s

The time taken to go downstream is x / (20 + s), and the time taken to go upstream is x / (20 - s). The total time taken for the journey is 2 hours, so we have:

x / (20 + s) + x / (20 - s) = 2

Simplifying and solving for x, we get:

x = (200s) / 41

Substituting this into the formula for average speed, we get:

average speed = 2x / (2x / (20 + s) + 2x / (20 - s)) = (40 - s^2) / (2s)

Substituting s = 2 km/h (from part a), we get:

average speed = (40 - 4) / 4 = 9 km/h

Therefore, the average speed for the whole journey when the boat travels 36 km downstream is 9 km/h.

Penjelasan:

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