Question

A boat is able to move through still water at 20 m/s. It makes a round trip to a town 3.0 km upstream. If the river flows at 5m/s ,the time required for this round trip is:
a) 120s
b) 150s
c) 200s
d) 300s
e) 320s​

Answer 1

V = d/t

so t = d/V

On the upstream part the boat is only going 20 m/s - 5 m/s = 15 m/s because the river pushing back.

t = 3000 m / 15 m/s = 200 s

And on the strip back the speed is 20 m/s + 5 m/s = 25 m/s because the river is now pushing you from behind adding to the speed

t = 3000 n / 25 m/s = 120 s

total time = 200 s + 120 s = 320 sec

Answer 2

Answer:

The time required for this round trip is e) 320s​.

Explanation:

Given,

A boat can drive through still water at 20 m/s.

To find,

The time required for this round trip is.

Step 1

Velocity of boat in still water , v = 20 m/s.

The velocity of the river,

V = 5 m/s.

In the provided question boat create a round trip to a town 3 km upstream.

Thus, Total time = time taken upstream + time taken upstream.

We know, $t=\frac{D}{v}$ ( here all have their usual meaning ).

Total time,

$t=\frac{3000}{(20-5)}+\frac{3000}{(20+5)}$( upstream velocity $=20-5=15 \mathrm{~m} / \mathrm{s}$.

downstream velocity$=20+5=25(\mathrm{~m} / \mathrm{s} )$

$t=200+120=320 \mathrm{~s} .$

Hence, The correct option is e) 320s​.

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