Question

if i weigh 100 lbs on earth how much would i weigh on halley's comet?

Answer 1

Were you really assigned this problem or are you just curious?

You need to know both the size of the solid head of the comet (the only place where you could stand), and its mass. The head is not spherical, having an oblong dimension of about 15 x 8 km. The mass is M = 2.2*10^14 kg. Because it is not spherical, your weight will depend upon where you are standing.

For an approximate value of your weight there, in Newtons
use a mean radius of R = 5500 m and the formula

W = G*M*m/R^2

where G is the universal constant of gravity, 6.67x10^-11 N*m^2/kg^2.
m = 45.5 kg is your own mass.

W = 0.022 Newtons
That is about 0.005 lb or 0.08 oz