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Three Piece explosion

A firecracker in a coconut blows the coconut into three pieces. Two pieces of equal mass fly off south and west, perpendicular to each other, at 20 m/s. The third piece has twice the mass as the other two.What is the speed of the third piece?

really boggled, no masses are given? i thought since the mass is double then the speed would be half of the speed of the 1st and 2nd pieces? anyone have an equation to help me out?
thanks
 
V

vsage

Resolve the momentums in the X and Y directions assuming the body is initially at rest:

[tex]\sum m_i v_i = 0[/tex] Here's the X direction (assuming east/west are the postive/negative x axis):

[tex] -20m + 2mv_x = 0[/tex]

and in the Y direction:

[tex] -20m + 2mv_y = 0[/tex]

It's easy to see what [tex]v_x[/tex] and [tex]v_y[/tex] are.
 
still dont understand, what do i put for the masses?
 
It doesn't matter what the masses are. The ratios are given. The masses will cancel out later once you have the relationship worked out.
 
so Vx = 10 and Vy = 10? after i solved in the equations
 

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