Given parameters:
First velocity = 2.50m/s
Time of travel = 3s
Second velocity = 1.50m/s
Unknown:
The displacement during the first interval = ?
Velocity is the displacement of a body with time. Displacement is a distance move in a specific direction by a body.
Velocity = 
So;
Displacement = Velocity x Time taken
Now input the parameter for the first velocity and time of travel;
Displacement = 2.5 x 3 = 7.5m
The displacement id 7.5m
If im correct the answer is gravity
and wind resistance if you lift it fast
~~~hope this helps~~~
~~davatar~~
Answer: The frequency = 1714.3Hz
Explanation: The solution can be achieved by using doppler effect formula.
Since the source is moving toward the observer, the velocity of the observer will be positive.
Please find the attached file for the solution