Is it vaccum at a height of 75,000 ft?

No. A vacuum does not exist at an altitude of 75,000 ft

Explanation:

There is naturally a decrease in air pressure as one goes higher into the atmosphere. However, vacuum conditions are not actually present within the atmosphere as there are still significant amounts of gases even at really high altitudes.

To prove this we know that planes cannot fly in a vacuum, because they need to burn air in order to gain propulsion from their engines.

One military plane - the SR-71 flew at about 90,000 feet.

This is a lot higher than 75,000 feet. For it to be able to at that altitude, it means that there was a significant quantity of air left even at 90,000 feet.

the body's situation won't change the forces are equal opposit and on the same body

the bal will not change its velocity.