What type of collision occurred?

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The discussion revolves around determining the type of collision between two identical blocks, A and B, where block A initially moves at 2 m/s and block B is at rest. After the collision, block A moves back at 1 m/s, while block B moves forward at 3 m/s, leading to an apparent increase in kinetic energy. The teacher suggests the collision is elastic, but some participants argue that the increase in kinetic energy might indicate an inelastic collision or that the question lacks sufficient information to determine the collision type. There is also speculation about the potential influence of external energy sources, such as compressed springs, affecting the outcome. Ultimately, the exact classification of the collision remains uncertain due to the complexities involved.
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Homework Statement


Block A is moving to the right at 2 m/s when it collides with an identical block B that is initially at rest. After the collision, block A is moving back to the left at 1 m/s and block B is moving to the right at 3 m/s. Which answer best describes the type of collision that occurred?
a) elastic
b) inelastic
c) perfectly inelastic
d) The answer to this question depends on the precise masses of the two blocks.
e) This question cannot be answered with the given information.

Homework Equations


(m1)(v1i) = (m1)(v1f) + (m2)(v2f)
KE = (1/2)mv^2

The Attempt at a Solution


my teacher said the answer was a, but i thought that the answer would be e, because the initial KE of the system is 2m, while the final KE is 5m. this means an increase in KE but i don't know if increase in KE can still be considered elastic.
 
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pacce said:

Homework Statement


Block A is moving to the right at 2 m/s when it collides with an identical block B that is initially at rest. After the collision, block A is moving back to the left at 1 m/s and block B is moving to the right at 3 m/s. Which answer best describes the type of collision that occurred?
a) elastic
b) inelastic
c) perfectly inelastic
d) The answer to this question depends on the precise masses of the two blocks.
e) This question cannot be answered with the given information.


Homework Equations


(m1)(v1i) = (m1)(v1f) + (m2)(v2f)
KE = (1/2)mv^2

The Attempt at a Solution


my teacher said the answer was a, but i thought that the answer would be e, because the initial KE of the system is 2m, while the final KE is 5m. this means an increase in KE but i don't know if increase in KE can still be considered elastic.
I agree with you. Energy has been added. But we don't know how much energy was added. We don't know if the collision was inelastic (it lost 1m of energy, say) and that energy was replaced plus additional energy (4m added) or if it was elastic and 3m of energy added.

Note: This could be a collision between two blocks with already compressed springs. Upon the colliding, the springs release and push the two blocks apart with spring force.

AM
 
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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