Time=speed/acceleration
Gravitaional Acceleration=9.8 m/s^2
Speed=24.5 m/s
Time=24.5/9.8=2.5 s
If the current takes him downstream we must find the resultant vector of the velocities:

Then if the river is 3000 m-wide the swimmer will have to pass:
1.3520747 · 300 = 4056.14 m t = 4056.14 m : 1 m/s
a ) It takes
4056.15 seconds ( 1 hour 7 minutes and 36 seconds ) to cross the river.
b ) 0.91 · 3000 =
2730 mHe will be 2730 m downstream.
Answer:
Instantaneous speed means speed at any instant
that means Speed is changing with time
You know speed is distance/time
So that means distance is also changing with time
So we take infinitesimal small distance per infinitesimal small time As we assume speed is constant in infinitesimal small time dt
So, we take speed = ds/dt
ds = infinitesimal small distance
dt = infinitesimal small time
As its ratio is equal to speed at any instant
Note : We are taking infinitesimal small distance
But :) we are taking infinitesimal small time also
As you know if denominator is small fraction is large So fraction always give large value
So it's not O ( this makes confuse to most of students)
So, thanks
Good question
Keep thinking like this :)