Question

(v) Two bricks of identical volume are sitting at the bottom of a swimming pool where the water depth is constant. Brick 1 has a density twice that of Brick 2. Which of the following is true in relation to the buoyancy forces on the bricks? (a) The buoyancy force is the same on both bricks. (b) The buoyancy force is twice as large on Brick 1 than on Brick 2. (c) The buoyancy forces are zero because the bricks are resting on the pool bottom.

(vi) Water flows full through two horizontal pipes of the same length and the same material. Both flows are turbulent and Pipe 1 is half the diameter of Pipe 2. If both pipes have the same mean flow speed, which of the following statements is correct regarding the pressure drop that occurs along the pipes? (a) Pipes 1 and 2 have the same pressure drop (b) Pipe 2 has the higher pressure drop (c) Pipe 1 has the higher pressure drop

Answer 1

First question

The buoyant force us equal to the weigjt ofvolume displaced by the brick. Here as given the two bricks are identical in volume so the buoyant force that will act on both bricks will be same for both bricks.

Second question

Head loss in pipe flow is given by

Head loss = { f ×L× V×V } / {2×g×D}

Here velocity V is same for both pipe and f will not vary much for turbulent flow the headloss will approximately inversely proportional to the diameter of the pipe so head loss will be more for the less dia pipe . So pipe 1 with less dia will have more headloss and hence the more pressure drop