Question

A 0.14-km wide river flows with a uniform speed of 4.0 m/s toward the east. It takes 20 s for a boat to cross the river to a point directly north of its departure point on the south bank. What is the speed of the boat relative to the water

Answer 1

Answer:

The right approach is "8.1 m/s". A further explanation is provided below.

Explanation:

According to the table,

Speed of Boat

= $\frac{s}{t}$

$V_b=\frac{140}{20}$

$V_a = 4 \ m/s$

$V_B = 7 \ m/s$

Now,

⇒  $(V_{relative})^2 = (7)^2+(4)^2$

or,

⇒  $(V_r)^2=49+16$

              $=65$

         $V_r=\sqrt{65}$

              $=8.1 \ m/s$