(a) Determine a differential equation for the velocity v(t) of a mass m sinking in water that imparts a resistance proportional to the square of the instantaneous velocity and also exerts an upward buoyant force whose magnitude is given by Archimedes€™ principle. See Problem 18 in Exercises 1.3. Assume that the positive direction is downward.

(b) Solve the differential equation in part (a).

(c) Determine the limiting, or terminal, velocity of the sinking mass.

Data from problem 18

A cylindrical barrel s feet in diameter of weight w lb is floating in water as shown in figure (a). After an initial depression the barrel exhibits an up-and-down bobbing motion along a vertical line. Using figure (b), determine a differential equation for the vertical displacement y(t) if the origin is taken to be on the vertical axis at the surface of the water when the barrel is at rest. Use Archimedes€™ principle: Buoyancy, or upward force of the water on the barrel, is equal to the weight of the water displaced. Assume that the downward direction is positive, that the weight density of water is 62.4 lb/ft³, and that there is no resistance between the barrel and the water.

Transcribed Image Text:

s/2 |s/2 surface }y(t) (b) (a)