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. If the squid has 1.75 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. How much kinetic energy does the squid create by tins maneuver?

Explanation / Answer

According to newtons 3rd law

Force applied on water by squid = force applied on squid by water

      F1 = F2

m1 * a1 = m2 * a2

where m1= mass of water  

          m2 = mass of squid

          a1 =acceleration of water

         a2= acceleration of squid

therefore,

      m1*(v1/t) = m2(v2/t)

     m1*v1 = m2 * v2

        v1= (m2/m1) * v2

       v1= (6.5/1.75 ) * 2.7

      v1= 10.028 m/s

therefore squid has to expel water by 10.028 m/s speed.

2. kinetic energy created by squid is equal to kinetic energy of water

    K.E. = (1/2)*m1*v1*v1

            = (1/2)* 1.75 * 10.028 * 10.028

            = 87.99 Joule

            = 88 Joule

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