Question: You have been hired as an intern for a plastics manufacturing company. When researching several types of plastics (Acrylic, HDPE, PET) to use for a new bottle design, the following facts were determined by a previous intern. Your boss has asked you to check the work of the previous intern. The previous intern listed several values of the specific gravity of PET. Which of the following is not a physically possible specific gravity of the plastic? Select all that apply. A. 187 B. 0.72 C. 72 D. 1.87
1. **State the problem:** We need to determine which values of specific gravity listed (187, 0.72, 72, 1.87) are not physically possible for PET plastic.
2. **Recall the definition and rules:** Specific gravity (SG) is the ratio of the density of a substance to the density of water at 4°C. It is a dimensionless quantity and typically for plastics, SG values are close to 1, usually between about 0.8 and 2.0.
3. **Analyze each value:**
- $187$: This is extremely high and unrealistic for any plastic. It would mean the plastic is 187 times denser than water, which is impossible.
- $0.72$: This is less than 1, meaning the plastic is less dense than water, which is possible for some plastics.
- $72$: This is very high and unrealistic for plastic, similar to 187.
- $1.87$: This is plausible as some plastics have SG close to 1.8.
4. **Conclusion:** The physically impossible specific gravities are $187$ and $72$.
**Final answer:** A. 187 and C. 72 are not physically possible specific gravities for PET plastic.