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

A) If the squid has 1.75 kg of water in its cavity, at what speed must it expel this water to suddenly achieve a speed of 2.70 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?

Answer 1

Solution:-

Given –

Squid mass – 7.00kg.

Speed – Speed can be thought of as the rate at which an object covers distance. A fast moving object has a high speed and covers a relatively large distance in a given amount of time. While a slow moving object covers a relatively small amount of distance in the same amount of time. Symbol of speed is ‘V’ and its SI unit is m/s.

Kinetic energy – The energy possessed by a body because of its motion, equal to one half the mass of the body times the square of its velocity.

K.E = ½*mv² and its SI unit is joule.

a)      Calculate speed

Given –

Mass – 1.75 kg

Speed- 2.70m/s

Initial momentum = 0

Final momentum, = 0 = 1.75kg *v *(7.00kg-1.75kg) * 2.70m/s

V = 8.1 m/s

b)     Calculate kinetic energy

K.E = ½ *1.75kg*(8.1)²*1/2 * (7.00-1.75) *(2.70)²

K.E = 57.40 + 19.13

K.E = 76.53 J

K.E = 77 J