Question

Usha swims in a $90\mathrm{m}$ pool. She covers $180\mathrm{m}$ in one minute by swimming from one end to the other and back along a straight path. Find the average velocity of Usha.

Answer 1

Step 1: Given

Length of the pool: $90\mathrm{m}$, Distance: $180\mathrm{m}$

Step 2:Find the average velocity of Usha
Average speed:
Speed $=\frac{\text{Distance}}{\text{TIme}}$
Or, Speed $=\frac{180}{60}$
Or, speed $=3\mathrm{m}/\mathrm{s}$
Velocity:
Velocity $=\frac{\text{Displacement}}{\text{Time}}$
Displacement $=0$ ( Since she comes back to the same place)

(Displacement is taken zero because, unlike distance, displacement is a vector quantity and it has direction. When Usha swims from one end of the pool to the other end her displacement is $90\mathrm{m}$ but when she swims back her displacement is $-90\mathrm{m}$, because she swims back in the opposite direction as a result, total displacement becomes $-90+90=0$ ).
So,
Average velocity $=0$
Hence, the average velocity of Usha is zero