Calculating Masses from Disc Explosion Velocities

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The discussion centers on calculating the mass ratio of two discs propelled apart by an explosion, with velocities of 9.0 m/s and 5.0 m/s. The ratio is derived using the principle of conservation of momentum, leading to the conclusion that the first disc has 5/9 the mass of the second. There is confusion regarding an answer key that states the mass ratio as 0.36, which does not align with the calculated ratio. Participants speculate on potential errors in either their calculations or the answer key. The conversation highlights the importance of understanding momentum in solving such physics problems.
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Two frictionless discs on air table, initially at rest, are driven apart by an explosion with velocities of 9.0m/s and 5.0m/s what is ratio of masses?
how do i get masses if i don't know Momentum ? +__+
 
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m1u1=m2u2 Since we want the ratio of m1 and m2 we make m2=m1*k(a constant)
m1(9m/s)=m1*k*5m/s
k=9/5 So the ratio of the two masses is that the 1st has the 5/9 of the seconds mass
 
ColdRifle said:
m1u1=m2u2 Since we want the ratio of m1 and m2 we make m2=m1*k(a constant)
m1(9m/s)=m1*k*5m/s
k=9/5 So the ratio of the two masses is that the 1st has the 5/9 of the seconds mass

the answer key says its 0.36 .. why's that?
 
I have no idea...maybe they made a mistake or I did one...lol
 
Thread 'Variable mass system : water sprayed into a moving container'

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}...
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