Question

A man swims a length of 100 m in still water with a speed of 1.2 m/s and returns the same length with a speed of 0.8 m/s. What is the average swimming speed of a man? What is his net velocity?

Answer 1

Definition of average speed and net velocity:

1. Average speed is defined as the ratio of total distance covered by a body with respect to the total time taken.
2. i.e. Average speed = total distance covered / total time taken.
3. Net velocity is defined as the total displacement of a body w.r.t. time.

Average Speed:

1. Let S₁ be the speed for the first 100 m = 1.2 m/s.
2. Let S₂ be the speed for a return trip of 100 m = 0.8 m/s.
3. Let T₁ be the time taken for the first 100 m and T₂ be the time taken for a return trip of 100 m.
4. Therefore, $$\begin{gathered} T_1=\frac{Dis\tan ce}{S_1}=\frac{100}{1.2}=83.34s \\ {T}_2=\frac{100}{0.8}=125s \end{gathered}$$
5. Therefore total time = 83.34 + 125 s = 208.34 s
6. Hence, average speed = 200 / 208.34 = 0.96 m/s.

Net velocity:

1. Since the net displacement is zero as the man returns to its initial position, therefore the net velocity is also zero.