Answer:
Time of flight of first rocket = 60 seconds
Time of flight of second rocket = 40 seconds
Step-by-step explanation:
Let the time of flight of first rocket be t1.
Since the second rocket is launched 20 seconds later, then it means that;
t1 = t2 + 20
Where t2 is the time of flight of the second rocket.
When destruction has occurred, it means that both of the rockets would have covered the same distance.
We know that;
Distance = speed × time
Thus;
2000t1 = 3000t2
We know that t1 = t2 + 20
Thus;
2000(t2 + 20) = 3000t2
2000t2 + 40000 = 3000t2
3000t2 - 2000t2 = 40000
1000t2 = 40000
t2 = 40000/1000
t2 = 40 seconds
Thus;
t1 = 40 + 20
t1 = 60 seconds