The mass will depend on the units used: 1 mm x 12 m x 12 m or 1 inch x 12 feet x 12 feet.
And having obtained the mass, the weight will depend on the strength of the force of gravity wherever the copper plate is located.
No 1964 silver quarter should have a copper layer and they all should be 90% silver, although it is possible that your quarter has tarnished or toned odd and just appeared to look non-silver. Both copper-nickel clad and silver quarters were produced in the mid-1960s with the clad ones being dated 1965 and later while the silver ones were dated 1964, so theoretically it could be struck on a copper-nickel planchet. I would weigh the coin, a silver one should weigh about 6.25 grams (naturally a worn quarter would weigh less) while a copper-nickel one should weigh much less, about 5.67 grams.
Modern copper-nickel dimes weigh 2.27 gm. Older (1964 and earlier) 90% silver dimes weighed 2.5 gm.
If you weighed 100 lbs on Earth you would weigh 112.5 lbs on Neptune.See related for how much you would weigh on other planets.
Copper pennies minted before 1982 weigh 3.11 grams.
It weigh about as much as a bowl of spaghetti
It is impossible to give an answer. For instance, a metre of copper wire, or a metre of a copper ingot?
Pre-1982 copper pennies weigh 3.11 grams. Pennies made since then are mostly zinc and weigh 2.5 grams.