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bharat91
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Homework Statement
An object with kinetic energy K explodes into two pieces, each of which moves with twice the speed of the original object.
Find the angles of the two velocities relative to the direction of motion before the explosion.
Modified question from "Essential University Physics 2nd Ed" by Richard Wolfson, Ch.9 Qu. 22 Page 151.
Homework Equations
Momentum: [itex]\vec{p} = m \times \vec{v} [/itex]
Momentum is conserved within an isolated system where no external forces are acting.
The Attempt at a Solution
Above diagram shows the object before explosion as "m1",
and the two objects created afterwards as "m2" and "m3".
[itex] m_1 = m_2 + m_3 [/itex]
Conservation of momentum gives us:
Horizontal: [itex] m_1 v = m_2\ 2v\ cos(θ) + m_3\ 2v\ cos(α) [/itex]
Vertical: [itex] m_2\ 2v\ sin(θ) = m_3\ 2v\ sin(α) [/itex]
Intuitively, if both resulting objects have the same velocity, and with no other data given, I would tend to think that the angles are the same as each other, and both masses are equal. Apparently this is the correct answer.
I don't understand why. I've tried a multitude of textbooks and worked examples. As far as I can gather, it is somehow related to the centre of mass of the system.
But in my mind, if I change the two resulting masses to be uneven, you can set the angles in such a way that the resulting centre of mass is still correct.
(As this is an isolated system with no external forces, the motion of the centre of mass remains unchanged after the explosion).
Manipulating the equations doesn't result in anything that I thought was useful in helping me along. I was hoping someone here could nudge me in the right direction, and help to explain the concepts involved? Thanks in advance.
Bharat.