Check your understanding 1. Paraffin wax has a density of 0.72 g/cm3. Explain why a lump of wax floats in water. .............................................................................................................................................. [1 mark] 2. Concrete has a density of 2.37 g/cm3. Does it float or sink in water? Explain why. .............................................................................................................................................. [1 mark] 3. An ice cube floats in water but most of the mass is under the surface. What does this suggest about the density of ice? .............................................................................................................................................. [1 mark] 4. Objects that float have mass. If they float, what does this show about the upthrust of the water compared with their weight? .............................................................................................................................................. [1 mark]
Spot the mistake 1. Emile is finding the density of a piece of oak. The mass is 14 g and the volume is 20 cm3. His answer is 1.43 g/cm3. What mistake has he made? .............................................................................................................................................. [1 mark] 2. Michelle is trying to find the volume of an irregular piece of cork. She fills a beaker full of water and lowers the cork carefully onto the top of the water, where it floats. She catches the water that overflows and measures its volume as 4 cm3. What mistake has she made? ........................................................................................................................................................... .............................................................................................................................................[2 marks] 3. Kareem is investigating density in an experiment. In his conclusion, he writes, Any solid with a density of less than 1 g/cm3 will float in any liquid. What mistake has he made? ........................................................................................................................................................... .............................................................................................................................................[2 marks]
Apply your understanding 1. Thousands of years ago, a Greek called Archimedes had a problem to solve. The King suspected that a crown was not pure gold. Archimedes knew that every metal has a different density. If he found the density of the crown, he would know whether it was pure gold. To find the density he needed to know the volume, but a crown is a complicated shape. The story goes that, after getting in a bath, he realised how to find the density of the crown. Suggest how he did it. ........................................................................................................................................................... .............................................................................................................................................[3 marks]
Physics 3
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