Help on this waves/phase difference question?

Question:

At the Chilbolton Observatory, the vertically-pointing Galileo RADAR measures the speed of falling snowflakes. The wavelength emitted and detected by Galileo is 3.2mm.

Two RADAR pulses are directed vertically towards the same falling snowflake with a time gap of 2.5ms. The two pulses leave the RADAR with the same phase. The first pulse returns to the detector with a phase of 180∘. The second pulse returns to the detector with a decreased phase of −160∘
Calculate the fall speed of the snowflake.

Assume that the fall speed is constant over the time between the two pulses arriving at the snowflake.

I dont have the answer so Im unsure of how to do it:

I got 0.0710 (2sf) when rearranging phase difference = 20pi rad to get "dist" in the equation to put into speed = dist/time (which is wrong)

Reply 1

lordaxil

The approach is described here.

Basically, you have to equal the phase shift to the extra number of wavelengths the first pulse travelled over second pulse due to the falling motion of snowflake.