Here is a fantastic question. No prizes for getting the right answer
(with explaination) but anyone fancy a go?

Given the following:
Ground speed 90kts
aircraft altitute 6000ft
VOR transmitter at mean sea level
Tan 40° = 0.839
assume 6000ft = 1nm

Theoretically, for approximately how many seconds would you expect the
morse identifier to be inaudible within the cone of silence if the
aircraft is tracking directly TO the VOR followed by its reciprical
directly away FROM the VOR?

A - 7 seconds
B - 20 seconds
C - 67 seconds
D - 100 seconds

None of the above. The "cone of slience" causes morse and any other
identifiers to become inaudible anytime the user is wearing one, as
demonstrated on several "Get Smart" episodes.