Kinetic energy after the collision

AI Thread Summary
The discussion focuses on calculating the kinetic energy and center of mass velocity for two colliding carts. The initial center of mass velocity is determined to be 0.332927 m/s, and the initial kinetic energy is calculated as 0.077634 J. After the collision, the kinetic energy is found to be 0.0568 J, indicating a loss of energy. The participants clarify that this scenario represents an inelastic collision, where kinetic energy is not conserved. The confusion arises from the difference in kinetic energy before and after the collision, highlighting the nature of inelastic collisions.
dg_5021
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Suppose the air cart to the left has a mass of .750kg and an initial speed of .455m/s. The cart to the right is initially at rest and has a mass of .275kg. Find the velocity of the center of mass. (a) before and (b) after the carts collide and stick together (c)Find to kinetic energy of the system before and after the collision.

(a)((.750kg)(.455 m/s) +(.275kg)(0m/s))/(.750kg+ .275kg) = .332927 m/s

(b)((.750kg)(.455 m/s) +(.275kg)(0m/s))/(.750kg+ .275kg) = .332927 m/s

(c)ki= (1/2) (.750kg)(.455m/s)^2 + (1/2)(.275kg)(0)^2 = .077634 J

i don't know how to get the kinetic energy of the system after the collision? can someone help me out?
 
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dg_5021 said:
i don't know how to get the kinetic energy of the system after the collision? can someone help me out?
You found the speed of the center of mass. Now you get to use it.
 
i really can't see that the amount of kinetic energy before and after the collision are equal.. They really are not. I'm really confused with this. I need help.

I computed for the amount of kinetic energy after collision and found it to be .0568 J. It does not really tally with the initial kinetic energy which is .0776 J. Please help.
 
Last edited:
samelliz said:
i really can't see that the amount of kinetic energy before and after the collision are equal.. They really are not. I'm really confused with this. I need help.

I computed for the amount of kinetic energy after collision and found it to be .0568 J. It does not really tally with the initial kinetic energy which is .0776 J. Please help.

Is this an elastic collision, or an in-elastic collision?
 
ok i got it. the example given above is an inelastic collision so the KE after it less than the KE before. But I've encountered lots of problems involving elastic collisions but really i never computed KE as equal.
 
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Thread 'Variable mass system : water sprayed into a moving container'

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