F = G.m.M/(r^2)F=G.m.Mr2
color(red)(g=10m/s^2g=10ms2
color(green)(M = 6times10^24kgM=6×1024kg (mass of the Earth)
color(blue)(G = 6.7times10^-11 Nm^2kg^-2G=6.7×10−11Nm2kg−2
color(orange)(m = 50kgm=50kg
color(violet)(r=6.4*10^6m = 6341kmr=6.4⋅106m=6341km (Radius of earth)
Weight of m=mg=50kg times10m/s^2=color(indigo)(500Nm=mg=50kg×10ms2=500N
We need to find r' such that "Weight"= color(purple)(250N
(half the weight of a 50kg mass)
F = (G*m*M)/(r^2)
=>color(purple)(250N) = (color(blue)(6*10^-11)*color(green)(6*10^24)*color(orange)(50))/(r')^2= (1.8*10^16)/(r')^2
=>(r')^2=(1.8*10^16)/(250)=color(grey)(7.2*10^30
=>r'=sqrtcolor(grey)(7.2*10^30)~~8485281m~~color(blue)(8485km
So, distance from earth's surface =r'-r
=color(blue)(8485km-color(violet)(6341km))~~2114km