Answer
Comet A will impact Earth first.
Work Step by Step
For Comet A:
Initial minimum distance from Earth: 600,000 kilometers
Decrease in minimum distance per orbital period: 40,000 kilometers
For Comet B:
Initial minimum distance from Earth: 450,000 kilometers
Decrease in minimum distance per orbital period: 25,000 kilometers
To calculate the number of orbital periods required for each comet to reach a minimum distance of zero (impact Earth), we can divide the initial minimum distance by the decrease in minimum distance per orbital period.
For Comet A:
Number of orbital periods to impact Earth = 600,000 kilometers / 40,000 kilometers = 15 orbital periods
For Comet B:
Number of orbital periods to impact Earth = 450,000 kilometers / 25,000 kilometers = 18 orbital periods
Therefore, based on the given information, Comet A will impact Earth first.
