Asked by victor
Pelicans tuck their wings and free-fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 15.0 m and cannot change its path once committed.
If it takes a fish 0.25 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.
If it takes a fish 0.25 s to perform evasive action, at what minimum height must it spot the pelican to escape? Assume the fish is at the surface of the water.
Answers
Answered by
drwls
The fish must spot the pelican when it is 0.25 s (or more) from hitting the water.
The pelican takes
t = sqrt(2H/g) = 1.75 s to hit the water if it starts its dive at H = 15 m.
Its vertical drop 1.50 s after starting the dive is y = (1/2)g*(1.50)^2 = 11.03 m
It is 15 - 11.03 = 4.97 m above the water surface at that time,
The pelican takes
t = sqrt(2H/g) = 1.75 s to hit the water if it starts its dive at H = 15 m.
Its vertical drop 1.50 s after starting the dive is y = (1/2)g*(1.50)^2 = 11.03 m
It is 15 - 11.03 = 4.97 m above the water surface at that time,
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