1kg equals about 2.2 lbs on Earth A) if you weigh 100 lbs what is your mass in kg, B) what is your weight in newtons

Question

This is a question on a homework assignment that I can't figure out. I'm not sure how to set up the equation

answer the problem by using the equation for force (F=ma) and (W=mg)

Answer 1

1 kg/2.2 lbs is the conversion factor. Given 100 lbs you can multiply by a ratio with lbs on the bottom and kg on the top, such that the lbs cancels out of the equation.

a) (100 lbs)*(1kg/2.2 lbs) = 100/2.2 kg = 45.5 kg

b) Weight is defined as mass multiplied by gravity. To get Newtons, the SI force unit, you must use SI units of mass and acceleration, so kg and m/s^2 respectivly. We just calculated the mass value in kg, so:

W=m*g = (45.5 kg)*(9.81 m/s^2) = 445.9 N

I don't see a need for Newtons second law (F_net=ma) in this problem.