Question 1153996
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<pre>

Since the problem asks about the resultant speed of both, it means that after collision, they move 
as one single body with the common speed.


    In Physics, such collision is called "inelastic" collision.


For such collisions, the Linear Moment conservation low is applicable:


    {{{m[1]*V[1]}}} - {{{m[2]*V[2]}}} = {{{(m[1]+m[2])*V}}}.    (1)


In formula (1), {{{m[1]}}} and {{{m[2]}}} are their masses;  {{{V[1]}}} and {{{V[2]}}} are their velocities before the collision;

the sum  {{{m[1]+m[2]}}} is the total mass of the "glued" body and {{{V}}} is their common speed after collision.


The sign " - " in formula (1) says that the bodies move initially in opposite directions.

The sign of the sum in the left side of (1) determine the direction, in which the resulting mass does move.


Substitute the given data into the formula (1)

    70*3 - 120*5 = (70+120)*V


and get

    V = {{{(70*3-120*5)/(70+120)}}} = -2.053.


<U>ANSWER</U>.  The resulting speed is -2.053 ft/s.  They move together in the same direction, as Hobbes moved before the collision.
</pre>

Solved.


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It is a typical Physics problem on inelastic collisions,

and from my post you learned now how to solve such problems.



Happy learning (!)