A motorboat can maintain a constant speed of 3333 miles per hour relative to the water. The boat makes a trip upstream to a certain point in 3535 minutes; the return trip takes 3131 minutes. What is the speed of the current?

2mph

Explanation:

In relative vector : Considering objects A and B

a) when two objects are moving in the same direction

Vab = Va + Vb

b) when two objects are moving in an opposite direction

Van = Va - Vb

Hence, this rule will be applied.

Speed upstream = ( 33-v ) opposite direction of the current

Downstream = ( 33+v ) same direction with the current

Distance = speed × time

Time upstream = 35/60

Time downstream = 31/60

From the formulae distance = speed × time

Upstream = ( 33-v ) × 35/60 1

Downstream = ( 33+V ) × 31/60 2

Equate 1 and 2

33-v) ×35/60 = 33+V) ×31/60

Multiply both side by 60

1155-35v = 1023+31v

1155-1023 = 31+35

132 = 66v

V = 2mph

explanation:

v=uf/(u-f)

= 5.-10/(5+10) convex lens has negative focal length