Question

6. A boat with speed of 1.20 km/h relative to the water is heading for a dock 2.29

Answer 1

Answer: 87 min

Explanation:

The speed of the boat $S_{boat}$ will be its speed relative to the river $S_{boat-river}$ plus the the speed of the river $S_{river}$:

$S_{boat}=S_{boat-river}+S_{river}$ (1)

$S_{boat}=1.20 km/h+0.384 km/h$ (2)

$S_{boat}=1.584 \frac{km}{h}$ (3)

On the other hand, the speed of the boat is given by a relation between its traveled distance $d$ and the time $t$:

$S_{boat}=\frac{d}{t}$ (4)

Isolating $t$ and knowing $d=2.29 km$:

$t=\frac{d}{S_{boat}}$ (5)

$t=\frac{2.29 km}{1.584 \frac{km}{h}}$ (6)

$t=1.445 h \frac{60min}{1 h}=86.74 min \approx 87 min$ (7)

Hence the time in minutes is 87 min.