A log starts floating freely down a river from a point P. At the same moment, a boat leaves a point Q, 28 km downstream of P, and moves upstream towards P. The boat moves at 16 km/hr in still water, and the river flows at 3 km/hr. After how long does the boat reach the log?
Answer & explanation
Correct answer: option 3
The correct answer is Option (3) → 1 hour 45 minutes
The log moves with the current at 3 km/hr, and the current takes the same 3 km/hr from the boat. So the gap closes at the boat’s still-water speed.
Log (downstream) \(=3\) km/hr
Boat (upstream) \(=16-3=13\) km/hr
The gap closes at \(3+13=16\) km/hr
Time \(\displaystyle =\frac{28}{16}=1.75\) hours \(=1\) hour 45 minutes