This procedure has been used to "weigh" astronauts in space:
a 42.5 kg chair is attached to a spring and allowed to oscillate. when it is empty, the chair takes 1.30 s to make one complete vibration. but with an astronaut sitting in it, with her feet off the floor, the chair now takes 2.54 s for one cycle.
what is the mass of the astronaut?

Mass of astronaut will be 119.7674 kg

Explanation:

We have given mass of the chair

When there is chair alone then time period of osculation

Now when astronaut sit on the chair then total mass

Now with astronaut time period is

For spring time period is given by

So

Squaring both side

Mass of astronaut will be 119.7674 kg

d. air pressure decreases as altitude increases.