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A 5-kg fish swimming 1 m/s swallows an absent minded 1-kg fish swimming toward it at a speed that brings both fish to a halt immediately after lunch. Show that the speed of the approaching smaller fish before lunch must have been 5 m/s.

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AMB000

Answer:

[tex]v_2=-5m/s[/tex]

Explanation:

If we call the big fish as 1 and the small one as 2 we write their initial linear momentum as:

[tex]p_i=m_1v_1+m_2v_2[/tex]

While their final linear momentum will be (since both are together we call their final velocity v):

[tex]p_f=m_1v+m_2v=(m_1+m_2)v[/tex]

But their final velocity is 0, so [tex]p_f=0[/tex], and since linear momentum must be conserved we have [tex]p_i=p_f=0[/tex], which means:

[tex]m_1v_1+m_2v_2=0[/tex]

We want the speed of the approaching smaller fish ([tex]v_2[/tex]), so:

[tex]m_1v_1=-m_2v_2[/tex]

[tex]v_2=-\frac{m_1v_1}{m_2}[/tex]

And just substitute our values:

[tex]v_2=-\frac{(5Kg)(1m/s)}{1Kg}=-5m/s[/tex]

Where the minus sign indicates that the small fish goes in the opposite direction as the big fish.

The speed of small fish is found out by linear momentum which is conserved before and after lunch.

The speed of small fish before lunch is 5 m/s.

What is the speed?

The speed of an object can be defined as the total distance covered by the object in a given time interval.

Given that the speed v1 of big fish is 1 m/s and mass m1 is 5 kg. The mass m2 of small fish is 1 kg.

The linear momentum of both the fish is given as,

[tex]p_1=m_1v_1 + m_2v_2[/tex]

Where p1 is the initial linear momentum and v2 is the speed of the small fish.

Both the fish are moving towards each other, so if v is the common velocity of both fish after meeting, then the final linear momentum will be given as,

[tex]p_2 = (m_1+m_2)v[/tex]

The linear momentum is conserved hence,

[tex]p_1 = p_2[/tex]

[tex]m_1v_1 + m_2v_2 = (m_1+m_2)v[/tex]

The final velocity of fish will be zero because they took a halt, so

[tex]m_1v_1 + m_2v_2 = 0[/tex]

[tex]v_2 = -\dfrac {m_1v_1}{m_2}[/tex]

[tex]v_2 = - \dfrac {5\times 1}{1}[/tex]

[tex]v_2 = -5\;\rm m/s[/tex]

The negative sign shows that the small fish moving in the opposite direction.

Hence we can conclude that the speed of small fish before lunch is 5 m/s.

To know more about speed and momentum, follow the link given below.

https://brainly.com/question/5794232.