Explanation:
As the astronaut jumps and reaches the highest point, he is momentarily at rest, i.e.
[tex]v=0[/tex]
We also know
[tex]u=3, s=15[/tex]
By the formula,
[tex]v^2-u^2=2as[/tex]
where a is the acceleration of objectc due to gravity,
[tex]0^2-3^2=2a(15)[/tex]
[tex]-9=30a[/tex]
[tex]a=-0.3 ms^{-2}[/tex]
where negative sign indicates a downwards acceleration.