Exercise 6.4
While practising for the snake boat race (Vallum kalli in Kerala), oarsmen are rowing a boat together. Out of these, row backwards to propel the boat forward. But by mistake, oarsmen row in the opposite direction. If each oarsman applies a horizontal force of N, what is the net force on the snake boat? (Ignore drag forces, air friction, etc.)
NCERT’s answer
$\displaystyle 18,000$ N in the forward direction
Net force \(\displaystyle = \) $\displaystyle 18,000$ N in the forward direction.
The $\displaystyle 95$ oarsmen rowing correctly push the boat forward with a total force \(\displaystyle = 95 \times 200\ \text{N} = 19{,}000\ \text{N} \).
The $\displaystyle 5$ oarsmen rowing the wrong way push it backward with \(\displaystyle 5 \times 200\ \text{N} = 1{,}000\ \text{N} \).
These are opposite in direction, so the net force is their difference, along the larger force:
\(\displaystyle F_{\text{net}} = 19{,}000\ \text{N} - 1{,}000\ \text{N} = 18{,}000\ \text{N} \), forward.