Squids and octopuses propel themselves by expelling water. They do this by keepi

Question

Squids and octopuses propel themselves by expelling water. They do this by keeping water in a cavity and then suddenly contracting the cavity to force out the water through an opening. A 6.50 kg squid (including the water in the cavity) at rest suddenly sees a dangerous predator. For related problemsolving tips and strategies, you may want to view a Video Tutor Solution of Recoil of a rifle. If the squid has 1.55 kg of water in its cavity, at what speed must it expel this water to instantaneously achieve a speed of 2.70 m/s to escape the predator? Neglect any drag effects of the surrounding water. upsilon = 8.62 m/s How much kinetic energy does the squid create by this maneuver?

Explanation / Answer

(A) Applying momentum conservation,

initial = final momentum of system

0 = (1.55 x v) - ((6.50-1.55) x 2.70)

v = 4.95 x 2.70 / 1.55

v = 8.62 m/s

(B) KE generated = KE of water + KE of squid

= (1.55 x 8.62^2 / 2) + (4.95 x 2.70^2 / 2)

= 75.7 J

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