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

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 2.50 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

Here,

mass of squid , m = 7.5 Kg

mw = 1.85 Kg

v = 2.50 m/s

let the speed of water is v1

part A)

Using conseravtion of momentum

mw * v1 - (m - mw) * v = 0

1.85 * v1 -(7.5 - 1.85) * 2.50 = 0

solving for v1

v1 = 7.64 m/s

the speed at which the water must be expelled is 7.64 m/s

B)

kinetic energy created by Squid = 0.5 * mw * v1^2 + 0.5 * (m - mw) * v^2

kinetic energy created by Squid = 0.5 * 1.85 * 7.64^2 + 0.5 * (7.4 - 1.85)* 2.5^2

kinetic energy created by Squid = 71.35 J

the kinetic energy created by Squid is 71.35 J

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