Question

Pelicans tuck their wings and free-fall straight down when diving for fish. Suppose a pelican starts its dive from a height of 17.0 m and cannot change its path once committed. If it takes a fish 0.25 s to perform evasive action, at what minimum height (m) must it spot the pelican to escape? Assume the fish is at the surface of the water. *significant figures matter in the final answer*

Answer 1

According to the concept of the motion in one dimenstional

Given that

height of pelican drive h=17 m

time for evasive action of fish t=0.25 sec

now we find the time taken pelican reach surface of water

time t1=(2h/g)^2=(2*17/9.8)^1/2=1.863 sec

so the time reaction between pelican and fish

reaction time T=1.863-0.25=1.613 sec

now we find the height at pelican catch the fish

height H=1/2*9.8*1.613^2=12.75 m

the minimum height the pelican to escape =h-H=17-12.75=4.25 m=4.3 m