What is the density of a roll of pennies containing 50 pennies?

Density is defined as:

Density = Mass/Volume

Now, density is an intensive property, this means that if you have 10 grams of a given material or 1000 grams of the same material, in both cases you will find the same density.

Then a roll of 50 pennies has the same density that a single penny.

The measures of a single penny are:

Mass = 2.5 g

Thickness = 1.52 mm

Radius = 9.525 mm

The coin is a cylinder, and the volume of a cylinder is:

V = pi*r^2*h

where:

pi = 3.14

r = radius = 9.525mm

h = thikness = 1.52mm

The volume is:

V = 3.14*(9.525mm)^2*1.52mm = 433.015 mm^3

The density will be:

D = 2.5g/433.015mm^3 = 0.00577 g/mm^3

10J

Explanation:

KE = (1/2)mv²

100J = (.5)(40kg)v²

v²=(100J)/(20kg)

v²= 5

KE = 5(.5)(4kg)

KE = 10J