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 7.50 kg squid (including the water in the cavity) at rest suddenly sees a dangerous predator.

a)If the squid has 1.85 kg of water in its cavity, at what speed must it expel this water to instantaneously achieve a speed of 2.30 m/s to escape the predator? Neglect any drag effects of the surrounding water.

b)How much kinetic energy does the squid create by this maneuver?

Explanation / Answer

a)we can solve this by law of conservation of momentum

initial momentum =0

final momentum=(7.5-1.85)(2.3)+1.85v

here v=speed of ejected water

initial momentum =final momentum

0=12.995+1.85v

v==12.995/1.85=-7.02m/s

b)kinetic energy created by squid=kinetic energy of squid+kinetic energy of water

=(1/2)((1.85x7.026^2)+(5.65X2.3^2))

=60.6J

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