Question

3. Aman swims a given length in still water with speed 1.2 m/s and returns the same length with speed 0.8 m/s. what
is the average speed of swim of the man? What is his average velocity?
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Answer 1

Answer:

Avg speed = $\frac{36}{25}$ m/s

Avg velocity = 0 m/s

Explanation:

Let distance Aman swims be x.

u (initial speed) = 1.2 m/s

initial time = $\frac{x}{1.2}$ = $\frac{10x}{12}$ = $\frac{5x}{6}$

v (final speed) = 0.8 m/s

final time = $\frac{x}{1.8}$ = $\frac{10x}{18}$ = $\frac{5x}{9}$

Total distance traveled = x + x = 2x

Avg. speed = $\frac{total distance traveled}{total time taken}$

                   = $\frac{2x}{5x/6 + 5x/9}$

                   = $\frac{2x}{25x /18}$    [The 18 goes in the numerator]

                   = $\frac{36x}{25x}$ = $\frac{36}{25}$ m/s

Total displacement = 0 m (Displacement is the shortest path from initial point to final point. As initial and final point is same displacement is 0 m)

Thus avg velocity = 0 (0 divided by anything is 0)