12. A ship travels 50 km due [N] and then turns and travels 30 km due [S] in 4.0 hours. What is its
average velocity?
a. 5.0 km/h [N]
b. 5.0 km/h [S]
c. 20 km/h [N]
d. 20 km/h [S]

a. 5.0 km/h [N]

Explanation:

The average velocity of an object is given by:

where

d is the displacement of the object

t is the time elapsed

The displacement is the change in position, so it corresponds to the vector connecting the initial position to the final position.

Here the ship travels 50 km North first, and then 30 km South: therefore, its displacement is

d = +50 + (-30) = +20 (North)

The time elapsed here is

t = 4.0 h

Therefore, the average velocity is

and the direction is the same as the displacement (North).

answer: the direction of the wind is expressed as the direction from which the wind is blowing. for example, easterly winds blow from east to west, while westerly winds blow from west to east.

explanation:

the correct choice is a .

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