Question

Wegut.

c) A body weighs 1.2N on the moon and 120N on
the earth. Calculate the density of the moon,
taking acceleration of free fall as 10ms on the
earth surface and gravitational constant as
6.67 x 10Nm’kg. The radius of the moon is
2740 km.​

Answer 1

We/Wm = ge/gm = 120N/1.2N

or

gm = ge/100 = 0.1 m/s^2

density = mass/volume = 3M/(4pir^3)

Re-arranging this equation, we get

M/r^2 = (4/3)×pi×(density)×r

From Newton's universal law of gravitation, the acceleration due to gravity on the moon gm is

gm = G(M/r^2) = G×(4/3)×pi×(density)×r

Solving for density, we get the expression

density = 3gm/(4×pi×G×r)

= 3(0.1)/(4×3.14×6.67×10^-11×2.74×10^6)

= 130.6 kg/m^3