Calculate the force of gravity between a newborn baby and the obstetrician, who is 0.5 m from the baby. Which exerts more gravitational force on the baby, Mars or the obstetrician? By how much?

Question

newborn baby- a mass of 3 kg

obstetrician- a mass of 100 kg

Answer 1

m₁ = 3 kg; m₂ = 100 kg; d = 0.5 m

Use F_g = Gm₁m₂/d² = (6.67 x 10^-11)(3)(100)/(0.5)² = 8.0 x 10^-8 N

The mass of Mars was not given, but it is 6.4171 x 10²³ kg.

The distance to Mars was not given and it varies a great deal. I will use the closest recent distance on Aug. 27, 2003, when it passed about 5.5758 x 10¹⁰ m from Earth.

Use F_g = (6.67 x 10^-11)(3)(6.4171 x 10²³)/(5.5758 x 10¹⁰)² = 4.1 x 10^-8 N

So the obstetrician exerts about twice as much gravitational force on the baby as Mars:

8.0 x 10^-8 N / 4.1 x 10^-8 N = 1.95 times greater