When a 2.0-kg object is suspended in water, it “masses” 1.5 kg. What is the density of the object?

Question

When a 2.0-kg object is suspended in water, it “masses” 1.5 kg. What is the density of the object?

Answer 1

density = mass / volume

and

volume = volume of water displaced =
=difference in weight/density of water = 0.5kg/ ( 1kg/L ) = 0.5L

so

density = 2.0kg / 0.5L = 4 kg/L

Answer 2

I think that the verbs in the question are backwards.

Mass is a property that is independent of all external factors, such as being underwater, being in space, etc.

Weight is the measure of a given gravitational field upon the mass of an object. The method for computing it's value was given by Newton's Universal Law of Gravitation.

However, there also exists apparent weight, which is actually quite different from the two. Essentially, apparent weight is the incorrect measurement that you obtain when you try to measure something's weight that results from experimental conditions.

If you try to measure the weight of something underwater, you will obtain an apparent weight, because water actually pushes up on the object when as it is submerged. So the object weighs less.

The way to calculate density from apparent weight is by using Archimedes Principle: the upwards force exerted upon a submerged object is equal to the mass of the displaced water.

So, the way to find the density is this: the force exerted upon the object is equal to the volume of the water displaced (there is a convenient relationship between the volume and mass of water: 1 L = 1 kg). So subtract the apparent weight from the real weight, the difference is the force of the water, which we know is equal to volume of water displaced, which then equals the volume of the object.

Density is defined as mass over volume. So divide the mass of the object by its volume.

I could spell it out for you more and solve it for you, but after all it is your homework . . .

Last thing I'll say is this. Mass is not a force. Weight is a force. Weight equals mass times "g=9.8". Units of mass: kilogram. Units of weight: newton.

Hope that helps.

Answer 3

3g/cc