What is the water level of Lake Ochechobee?

I am in a boat on a fresh water lake. In my hand is a rock. I throw the rock into the lake. How is the lake's water level affected?

• Answer:

  It goes down.. the reason is buoyancy by Archimedes' principle, buoyant force = weight of displaced liquid = m*g = rho*V*g #if rho and g of the fluid are constant (which is the case when u r in a lake) it is the variation in buoyant force that affects the volume of displaced fluid buoyant force arises as a result of P diff bet the top and bottom surfaces of an object put in a liquid.. if its floating, one side its ATM P and other side P on the lowest surface of the object inside the liquid... if its immersed, due to Pascal Law, 2 diff P are goin to act Situation A: rock in ur hand ur boat floats... so the buoyant force is capable of counteracting the weight of the entire boat (no matter whatever weight is der... u, rocks or anything.. u jus have 2 keep the structural integrity of the boat so that it floats - that's why we avoid overloading) say weight of rocks is W1 and the rest weight W2... now B.F. = W1+W2 Situation B: rock thrown in water consider W1 and W2 separately... for W2, as it is still floating, B.F.2 = W2 for W1, as it has sunk, tis clearly implies that ur B.F.1 was not able to cancel W1.. that's why the rock has sunk.. the difference between these two is trimmed out and the rock is maintained in equi. by the normal reaction the rock has at the ground... hence B.F.1 = W1 - R So, B.F. = B.F.1 +B.F.2 = W1+W2-R By point #, we can see that second situation displaces less vol than the first So, water level goes down