Question

two bodies of masses m and 4m are places at a distance r. The gravitational potential at a point on the line joining them where the gravitational field is zero.
A)-4Gm/r
B)-6Gm/r
C)-9Gm/r
D) zero

Answer 1

d zero..........




... ......

Answer 2

Let the point be the position when the gravitational field is zero
Gmx2=G(4m)(r−x)2Gmx2=G(4m)(r−x)2
1x=2(r−x)1x=2(r−x)
r−x=2xr−x=2x
x=r3x=r3
the point P is at a distance r3r3 from mass m and 2r32r3 from mass 4m
V=−GMr3−G(4m)2r3V=−GMr3−G(4m)2r3
=−9GMr=−9GMr
Hence d is the correct answer.