Choose the lens having the shortest focal length.
a.

b.
c.
Question 2A 0.20-km wide river has a uniform flow speed of 3.0 m/s toward the east. A boat with a speed of 8.0 m/s relative to the water leaves the south bank and heads in such a way that it crosses to a point directly north of its departure point. How long does it take the boat to cross the river?
a. 29 s
b. 23 s
c. 25 s
d. 27 s
e. 17 s