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Problem 15 Easy Difficulty

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. $A 6.50-k g$ squid (including the water in the cavity) at rest suddenly sees a dangerous predator. (a) If the squid has 1.75 $\mathrm{kg}$ of water in its cavity, at what speed must it expel this water to suddenly achieve a speed of 2.50 $\mathrm{m} / \mathrm{s}$ 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

(a) $+6.79 \mathrm{m} / \mathrm{s}$
(b) $55.2 \mathrm{J}$

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Video Transcript

{'transcript': "So in this question we have a squid and it has water and say it and has a total mass off 6.5 kilograms. Because it's a some predator, it pushes the water out on DH due to the reactionary forces most forward. So after which is the water out, the squid is moving forward with the velocity 2.5 meters per second on the water. Let's say is moving with the velocity V. We know that water has mass 1.75 kilograms and hence the square would have 6.5 minus 1.5 4.75 kilograms. Wait no to find the velocity of the water. We simply is conditional. Mourned him because there are no other external forces. Thie horizontal movement of must be conserved and the initial random zero because there is no motion and the final moment has to part the moment about the squid on the water. But the squared then went to Miss Mass. 4.75 times the velocity 2.5 less For the water, it's 1.75 the mass times the velocity V. This must be equal to zero because the final and initial momentum are the same. Discusses B is 2.5 times 4.75 You added by 1.75 is equal to you. 6.78 I'm sorry. 79 meters per second. Now that you know this, I'm sorry. There's a minus Sign here. This minus sign implies that the velocities in the backward action. Now that we know this, we simply want to find the kind of energy. I'm sorry, the energy expended by the square integrating this motion now, Initially, the kind of energy is zero. And if we find out the final kind of unity, the energy expended by the square will simply be the final indignity, which is for the squared. It's half times 4.75 I'm still 0.5 square because in our kind of catchy is half and B squared and then with someone all the objects less or the water it is half times 1.75 times 6.79 square, which turns out to be 55 point to Jules"}

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