I have these little pieces of steel:
I can weigh the whole thing on a scale (the one with lines on it is 14.07g), but I just want to weigh part of it (e.g. the green line to the end i.e. excluding the red X).
The weight is not uniformly distributed along the length, so while I could calculate an estimate based on the position of the green line, it wouldn't be sufficiently accurate.
Is there some nondestructive way to weigh just that specific portion of it?
Best Answer
Use a balance to get the mass of the whole steel object. Then, fill a 100 ml graduate cylinder exactly to the 50 ml mark. Place the steel in the graduate cylinder, obtain the new reading, and subtract 50 ml from that reading to obtain the volume of the steel part. From that information, calculate the density of the steel as $\rho = \frac{m}{V}$.
Next, tie a string around the right end of the steel part. Make sure that the graduate cylinder again has exactly 50 ml of water in it. Submerge the steel part up to the green line, obtain the new graduate cylinder reading, and calculate the volume of the steel part that was submerged. Using that volume and the previously calculated density, calculate the mass of the submerged portion.