Answer:[tex]\frac{g}{2}[/tex]
Explanation:
Given
mass of stone[tex]\left ( m\right )[/tex]=0.250 kg
Let initial velocity with which it is thrown upward is u
therefore after time t it's velocity is zero at highest point
t=[tex]\frac{u}{g}[/tex]
where g= gravity at earth
therefore [tex]T=2\times \frac{u}{g}[/tex]-------1
Now same thing is done in Planet X where gravity is g'
therefore time taken by stone to reach surface is
[tex]T'=T=2\times \frac{u}{g'}[/tex]-------2
Divide 1 & 2
[tex]\frac{T}{T'}[/tex]=[tex]\frac{g'}{g}[/tex]
[tex]\frac{1}{2}[/tex]=[tex]\frac{g'}{g}[/tex]
g'=[tex]\frac{g}{2}[/tex]