A rock is suspended by a light string. When the rock is in air, the tension in the string is 55.9 N. When the rock is totally immersed in water, the tension is 37.6 N. When the rock is totally immersed in an unknown liquid, the tension is 20.4 N. What is the Density of the unknown liquid. -When I looked at this problem, I though we needed to know the volume of the rock. Can someone show me how to do it without the volume of this rock?