Answer:
1. Two materials that can be scratched by an iron nail are <u>zinc</u> and <u>aluminum</u>
2. A substance that can be scratched by an iron nail but not a penny is;
Nickel
Explanation:
The hardness of a material can be defined as its ability to resist being plastically deformed at a location due to mechanical scratching, abrasion or indentation
The Mohs hardness scale provides a ranking of materials in the order of hardness with a material having a higher Mohs hardness number being able to scratch other materials which have a lower Mohs hardness number
1. From the Mohs scale of hardness, iron which has an harness number of 4.5 can scratch zinc which has an harness number of 2.5, and iron can also scratch aluminum which has an hardness number of 2.5 to 3
2. A penny is made from copper plated material and will have an outer layer hardness of copper which has an hardness number of 3 on the Mohs scale
Therefore, a penny cannot scratch a material mode of nickel which has an hardness number of 4, while iron which has an hardness of 4.5 will scratch a nickel material
. Thus, the equation for velocity is 
.