physics question

hi, please could I have help on 10c, I don't understand the markscheme/
paper: https://www.physicsandmathstutor.com/pdf-pages/?pdf=https%3A%2F%2Fpmt.physicsandmathstutor.com%2Fdownload%2FPhysics%2FA-level%2FTopic-Qs%2FCAIE%2F13-Gravitational-Fields%2FSet-F%2FGravitation.pdf (page 15)
markscheme: https://www.physicsandmathstutor.com/pdf-pages/?pdf=https%3A%2F%2Fpmt.physicsandmathstutor.com%2Fdownload%2FPhysics%2FA-level%2FTopic-Qs%2FCAIE%2F13-Gravitational-Fields%2FSet-F%2FGravitation%20MS.pdf (page 4)
thanks!

Which part of the MS that you don't understand?

for the yellow part, I don't get how they are related and for the blue part, I'm not sure how they got from the first line to the next?

For yellow part:
At A level, gravitational field strength is by “definition” taken as g = GM/r² NOT a constant value because r changes.
Since the object moves through a short distance h near to the surface and g is relatively constant when the object moves through a short distance h.
For the blue part, r₁ is the radius of the planet and r₂ = r₁ + h and apply these info, you can get the result.

I understand the yellow part now but for the blue part, I substituted r₂ = r₁ + h into the line above to get GMm(h/r(h+r1)) but I don’t get how this is related to g=GM/r^2? Thanks

hi, please could I have help on 10c, I don't understand the markscheme/
paper: https://www.physicsandmathstutor.com/pdf-pages/?pdf=https%3A%2F%2Fpmt.physicsandmathstutor.com%2Fdownload%2FPhysics%2FA-level%2FTopic-Qs%2FCAIE%2F13-Gravitational-Fields%2FSet-F%2FGravitation.pdf (page 15)
markscheme: https://www.physicsandmathstutor.com/pdf-pages/?pdf=https%3A%2F%2Fpmt.physicsandmathstutor.com%2Fdownload%2FPhysics%2FA-level%2FTopic-Qs%2FCAIE%2F13-Gravitational-Fields%2FSet-F%2FGravitation%20MS.pdf (page 4)
thanks!