He developing fetus reaches the age of viability weeks after conception, during the period.

The developing fetus reaches viability 26 weeks after conception during the embryonic development period.

Explanation:

Doctors use the term "fetal viability" to describe when vital organs such as the kidneys, lungs or heart are well enough formed to function with or without medical care, in which case the baby can be assured that has a chance of surviving outside the womb. This event usually occurs around 26 weeks of pregnancy during embryonic development, when the fetus could already be born. Otherwise, the birth would be too premature, or unviable, with no or very low probability of success.

the speed increase from w to x due to increased gravity force

the speed decreases from x to y due to decrease in gravity

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