Problem 47P

(a) Show that the flow velocity measured by a venturi meter (see Fig. 10–30) is given by the relation

(b) A venturi tube is measuring the flow of water; it has a main diameter of 3.0 cm tapering down to a throat diameter of 1.0 cm. If the pressure difference is measured to be 18 mm-Hg, what is the velocity of the water?

FIGURE 10–30 Venturi meter.

ANSWER:Weight of the elevator is 2500 N.By definition of weight, it is the normal reaction an object gets.So, N = mg = mass × 9.8 = 2500 mass = 2500/9.8 = 245 kg .But here we should not get the value for mass. It’s useless.We know the weight, which is the normal reaction and it’s the force itself. And wealso know that force times speed is the power. So, let’s put the values in the formula. P = force × velocity P = 2500 × 8 = 20000 watts.CONCLUSION:So, the motor must supply a power of 20000 watts.