A river flows at 2.50 m/s to the north, while a boat travels from south to north with a
constant velocity of 12.5
m/s relative to the water.
What is the velocity of the boat relative to an
observer at rest on the shore?

15 m/s towards the North

Explanation:

we need to add both velocities to find the effective velocity from the point of view of an observer at rest on the shore:

2.5 m/s + 12.5 m/s = 15 m/s pointing North

5 w for 1hr = 5x60x60 joules=300x60=3000x6=18,000j as total energy conversion. efficiency of bulb needed for radiant to thermal within 18000