Question

4) A boat travelled 336 km downstream with the current. The trip downstream took 12 hours.a) Come up with an equation to describe this relationship b) If the current is moving at 2 km/h, how fast is the boat moving from its engine?

Answer 1

We have a distance of 336 km and a time to travel that distance that is 12 hours.

We can write the distance traveled in function of time as a proportional relationship, with constant of proportionality:

$k=\frac{336\operatorname{km}}{12h}=28\frac{\operatorname{km}}{h}$

a) Then, the equation becomes:

$d=28\cdot t$

with d (distance) in km, and t (time) in hours.

Answer: d=28*t

b) If the current is 2 km/h and assuming the current is adding to the speed of the boat, we know that the average speed (28 km/h) is the sum of the current speed and the engine speed, so we can calculate the engine speed as:

$\begin{gathered} v_c+v_e=28 \\ v_e=28-v_c=28-2=26 \end{gathered}$

Answer: The speed coming from the engine is 26 km/h.