Physics, density problem... help!?

Question

A bottle has a mass of 0.2kg and a volume of .001 m3. How much sand of density 1500 would you have to put inside the bottle to just make it sink in water of density 1000? The weight of the remaining air in the bottle can be ignored.

Help? Thanks!

Answer 1

Assuming that the 0.001 m3 (= 1 liter) means the external volume (not the internal capacity), the bottle will sink if the weight of the empty bottle plus the sand equals 1 kg.  So you have to put 0.8 kg of sand (0.0005333 m3) inside the bottle.