For this case you must first know the definition of density.
D = m / v
where,
m: mass
v: volume.
You can then write the following hypothesis:
IF you know two physical characteristics of an object then you can determine the density. First weigh the object, THEN measure its volume BECAUSE the density is the quotient between the mass and the volume of an object.
Oh my gosh ! Resisting the force of gravity always DOES involve doing work.
If no work is being done, then you're NOT resisting the force of gravity.
Example:
-- ball rolling on the floor . . . no work
-- ball rolling up a ramp . . . work being done
-- ball rolling down a ramp . . . work being done, BY gravity
Newton’s second law gives us the relationship of force F,
mass m and acceleration a. The formula is given as:
<span>F = m a -->
1</span>
However we also know that the relationship of mass m,
density ρ, and volume V is:
<span>m = V ρ -->
2</span>
Therefore substituting equation 2 to equation 1:
F = ρ V a = ρ V g
where a is acceleration due to gravity, ρ is density of
water and V is the volume of the casting, therefore:
F = (1x10^-3 kg/cm^3) (4840 cm^3) (9.8 m/s^2)
F = 47.432 kg m/s^2
F = 47.432 N
Going back to equation 1:
47.432 N = m (9.8 m/s^2)
m = 4.84 kg
<span>Hence the weight of the final casting is 4.84 kg</span>
