Solutions

1. The paddling pool in the photo is 8ft diameter and 1.5 ft deep. If it was filled with oil instead of water would its mass be more or less? Calculate the difference in mass if filled with water and oil.

density of oil = 800 kgm-3
density of water = 1000 kgm-3 Hint:

• The density of oil is less than water so the same volume of oil will be less than the volume of water
• First convert the lengths into meters and calculate the volume in m3
• The pool is a cylinder so V = πr2l
• Density = mass/ Volume
• If you rearrange this you can get a formula for mass
• Calculate the mass of oil and water with a volume = volume of the pool

Solution: 2.  63g of Copper contains 6 x 1023 atoms. What is the approximate size of an atom?

Density of copper = 9 gcm-3 Hint:

• Copper is made of atoms so if you divide the volume of copper by the number of toms you'll get the volume of an atom.
• First rearrange ρ=m/v to find the volume of copper.
• divide volume by the number of atoms.
• find the cube root of the volume to give the "size".

Solution: 3. Calculate the length of a 30kg reel of 5mm thick copper wire. Hint:

• Wire is a cylinder so volume =πr2l
• Convert the units of density to kgm-3
• Find the volume of the wire
• rearrange the equation for volume of a cylinder to find the length.

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