Answer:
Force of sun on earth can be written:
F = G M m / R^2
Centripetal force on earth can be written:
F= m w^2 R
Equating these:
G M / R^2 = w^2 R
Or w^2 = G (M / R^3)
Since no/ days per year is proportional to w (time for 1 revolution)
Increasing M (mass of sun) would increase w or decrease length of year
Increasing the mean radius R would decrease w or increase length of year
