Answer Key Homework 1 - Density
To-Do Date: Feb 12 at 8:00amThis is the answer key for Assignment 1 - Density. Once posted, no late homework assignments will be accepted under any circumstances.
- The density of water is 1.0 grams per cubic centimeter. The density of gasoline is 0.7 grams per cubic centimeter. The two liquids do not mix. If you pull into a gas station with 3 gallons of gas in the tank of the car and somehow pump water into your gas tank what will happen?
Water has a higher density than gasoline. We would, therefore, expect the water to sink to the bottom of the gas tank displacing the gasoline already in the tank. The water would then end up be drawn into the engine and you'd be stuck with a big repair bill.
- Mercury has a density of 13.6 grams per cubic centimeter. Iron has a density of 7.9 grams per cubic centimeter. If you place an iron cannon ball into the vat of mercury will it: (a) sink to the bottom (b) float in the center of the vat or (c) float near the top of the vat? Why?
(c) the iron ball will float near the top of the vat
The iron cannon ball has approximately half the density of the mercury, therefore, it floats. In order to sink to the bottom of the vat, the cannon ball would have to have a density greater than the mercury (>13.6). In order to float in the middle of the vat, the cannon ball would have to have the same density as the mercury (=13.6).
- Using the table of densities below answer the following question:
In Arkansas and some other places there are natural diamonds lying around on the surface of the ground. Explain how you could quickly separate diamonds from a shovelful of common gravel containing mostly quartz and feldspar, using a liquid of appropriate density. Write your answer carefully, detailing the steps. Please use the chart below to answer this question.
| Substance | Density gm/cc (grams/cubic centimeter) |
Density lbs/cu.ft (pounds/cubic foot) |
|---|---|---|
| Mercury | 13.6 | 849 |
| Bromine | 3.1 | 195 |
| Water | 1.0 | 62 |
| Alchohol | 0.8 | 49 |
| Gasoline | 0.7 | 42 |
| Feldspar | 2.6 - 2.8 | 159 - 172 |
| Quartz | 2.65 | 165 |
| Diamond | 3.0 - 3.5 | 188 -220 |
You are given only 5 liquids to choose from. Your goal is to select a liquid with a density that will help separate the diamonds from the feldspar/quartz. Bromine has a density of 3.1. If you throw a shovel full of gravel in a bucket of bromine the feldspar (density 2.6 -2.8) and the quartz (density 2.65) will rise toward the top of the bucket since they are less dense than the bromine. Most of the diamonds (density 3.0 - 3.5) will sink to the bottom of the bucket since they have a density greater than the bromine (3.1). However, there may be diamonds that will float in the center of the bucket or slightly above because their density is the same as bromine. Not a perfect solution (especially since no one wants to mess with toxic bromine) but it will still "sort" the diamonds from the gravel.
- What is the oblateness of a watermelon with a length of 15 inches and a diameter of 10 inches? Remember the formula for oblateness: Ob = (max - min) / (max + min) x 100 We express oblateness as a percent.
The Maximum dimension from our watermelon is 15 inches and the minimum is 10. Plugging those numbers into the formula:
15-10 ÷ 15+10 = 5 ÷ 25 = 0.2
0.2 x 100 = 20%