Chapter P.2, Problem 16P

Squid Propulsion

Squid usually move by using their tins, but they can utilize a form of “jet propulsion,” ejecting water at high speed to rocket them backward, as shown in Figure II.I. A 4.0 kg squid can slowly draw in and then quickly eject 0.30 kg of water. The water is ejected in 0.10 s at a speed of 10 m/s. This gives the squid a quick burst of speed to evade predators or catch prey.

FIGURE II.1

This form of locomotion is speedy, but is it efficient? The energy that the squid expends goes two places: the kinetic energy of the squid and the kinetic energy of the water. Think about how to define “what you get" and “what you had to pay"; then calculate an efficiency for this particular form of locomotion. (You can ignore biomechanical efficiency for this problem.)