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. (a) If the squid has 1.75 kg of water in its cavity, at what speed must it expel this water suddenly to achieve a speed of 2.50 m/s to escape the predator? Ignore any drag effects of the surrounding water. (b) How much kinetic energy does the squid create by this maneuver?

Respuesta :

Answer:

6.78571 m/s

55.13387 Joules

Explanation:

[tex]v_s[/tex] = Velocity of squid = 2.5 m/s

[tex]v_w[/tex] = Velocity of water

[tex]m_w[/tex] = Mass of water = 1.75 kg

Mass of squid

[tex]m_s=6.5-1.75=4.75\ kg[/tex]

Momentum of squid

[tex]p_s=m_sv_s\\\Rightarrow p_s=4.75\times 2.5\\\Rightarrow p_s=11.875\ kgm/s[/tex]

As the momentum of the system is conserved

[tex]p_s+p_w=0\\\Rightarrow p_s=-p_w\\\Rightarrow 11.875=-p_w\\\Rightarrow 11.875=-m_wv_w\\\Rightarrow v_w=-\frac{11.875}{1.75}\\\Rightarrow v_w=6.78571\ m/s[/tex]

The speed of the water is 6.78571 m/s

Kinetic energy the squid creates is given by

Kinetic energy of the squid + Kinetic energy of water

[tex]K=K_s+K_w\\\Rightarrow K=\frac{1}{2}(m_sv_s^2+m_wv_w^2)\\\Rightarrow K=\frac{1}{2}(4.75\times 2.5^2+1.75\times 6.78571^2)\\\Rightarrow K=55.13387\ J[/tex]

Kinetic energy the squid creates by this maneuver is 55.13387 Joules

(a) The speed of water to escape the predator  [tex]V_w=6.758\frac{m}{s}[/tex]=

(b) Kinetic energy = 55.13J

What will be the speed of water and the KE of squid?

It is given that

Velocity of squid  [tex]V_S[/tex]= 2.5 m/s

Velocity of water  [tex]V_w=?[/tex]

Mass of water  [tex]m_w[/tex]  = 1.75 kg

The mass of the squid will be given as

[tex]m_s=6.5-1.75=4.75kg[/tex]

Momentum of squid

[tex]P_s=m_sv_s=4.75\times2.5=11.875\frac{kgm}{s}[/tex]

Since by the conservatiom of momentum

[tex]P_s+P_w=0[/tex]

[tex]P_s=-P_w[/tex]

[tex]11.875=-P_w[/tex]

[tex]-m_w v_w=11.875[/tex]

[tex]V_w=-6.785\frac{m}{s}[/tex]

So the speed of the water is 6.78571 m/s

The kinetic energy created by squid will be

The kinetic energy of the squid + Kinetic energy of water

[tex]K=K_s+K_w[/tex]

[tex]\dfrac{1}{2} (m_sv_s^2+m_wv_w^2)[/tex]

[tex]\dfrac{1}{2} (4.75\times(2.5)^2+1.75+(6.78^2))[/tex]

[tex]KE=55.13J[/tex]

Thus

(a) The speed of water to escape the predator  [tex]V_w=6.758\frac{m}{s}[/tex]=

(b) Kinetic energy = 55.13J

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