The time taken by the swimmer was 1 hour.
Why?
Since the swimmer is maintaining an angle of 150° while he was swimming, there were two components of the speed (horizontal and vertical). If we want to calculate the time taken by him to cross the river, we need to calculate the vertical speed and consider that the flow's speed is compensated by his horizontal speed.
We can calculate both components of the speed using the following formula:

Now, calculating we have:

Therefore, we have that the horizontal speed is compesating the flow's speed while his vertical speed is used to cross the river which is 1 Km wide.
Hence, we have that the tame taken is:

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This is not something that waves do because they need a medium to travel through, while particles do not.
<h3>How light travels in space?</h3>
A light travels without any medium while on the other hand, a medium is required for sound waves to move from oe place to another. Sound is a mechanical wave that cannot travel through a vacuum.
So we can conclude that electromagnetic waves like light do not require medium for its propagation.
Learn more about light here: brainly.com/question/19697218
Answer:
Atmospheric pressure is commonly measured with a barometer. In a barometer, a column of mercury in a glass tube rises or falls as the weight of the atmosphere changes. Meteorologists describe the atmospheric pressure by how high the mercury rises.
Explanation:
Hope it helps you
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If we assume that the acceleration is constant, we can use on the kinematic equations:
Vf = Vi + a*t = 15 + 3*4 = 27 m/s