Very simple high school phisics question

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A stationary object explodes into two fragments, with one 4.0 kg fragment moving west at 3.0 m/s. The remaining 2.0 kg fragment's speed and kinetic energy can be determined using conservation of momentum, rather than assuming equal kinetic energy for both fragments. The assumption that kinetic energy is divided equally is flawed because the explosion applies forces differently to each fragment. The discussion emphasizes the importance of using momentum conservation in solving such problems. Understanding the dynamics of the explosion is crucial for accurate calculations.
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A stationary object explodes into two fragments. A 4.0 kg fragment moves westward at 3.0 m/s. What are the speed and kinetic energy of the remaining 2.0 kg fragment?
why can't i assume the kinect enegery of each object is the same?I loked at it and assumed 1/2mv^2 for object 1 should equal object 2 subsituded numbers got 18J=1/2 2 v^2

but the answer says its 36J's
 
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A better question to ask is "why did I assume kinetic energy is divided equally?". Try to think about the explosion. The explosion forces the pieces away. You may assume that the force on both pieces is the same. How long does the force act on each particle, and how far does it act?
 
Thanks

thats simple enough the t part for how long the force was acting... :P
ill just solve it with momentum.
 
If you solve this with conservation of momentum, you can figure out the problem. I've come to realize that solving things with conservation of momentum is a better way to start in these sort of macro-classical mechanic problems.
 
Thread 'Variable mass system : water sprayed into a moving container'
Starting with the mass considerations #m(t)# is mass of water #M_{c}# mass of container and #M(t)# mass of total system $$M(t) = M_{C} + m(t)$$ $$\Rightarrow \frac{dM(t)}{dt} = \frac{dm(t)}{dt}$$ $$P_i = Mv + u \, dm$$ $$P_f = (M + dm)(v + dv)$$ $$\Delta P = M \, dv + (v - u) \, dm$$ $$F = \frac{dP}{dt} = M \frac{dv}{dt} + (v - u) \frac{dm}{dt}$$ $$F = u \frac{dm}{dt} = \rho A u^2$$ from conservation of momentum , the cannon recoils with the same force which it applies. $$\quad \frac{dm}{dt}...
I was thinking using 2 purple mattress samples, and taping them together, I do want other ideas though, the main guidelines are; Must have a volume LESS than 1600 cubic centimeters, and CAN'T exceed 25 cm in ANY direction. Must be LESS than 1 kg. NO parachutes. NO glue or Tape can touch the egg. MUST be able to take egg out in less than 1 minute. Grade A large eggs will be used.
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