Looking for deltaK, change in total kinetic energy

AI Thread Summary
The discussion focuses on calculating the change in total kinetic energy (ΔK) for a collision between two pucks on a frictionless air table. Puck A, with a mass of 0.253 kg, moves towards stationary puck B (0.373 kg), resulting in post-collision velocities of 0.124 m/s for puck A and 0.650 m/s for puck B. Participants initially calculated ΔK as -0.007 J but later realized that significant figures and rounding errors may have affected their results. The correct calculation requires using the appropriate number of significant figures, as the initial values provided have three significant figures. The conversation emphasizes the importance of precision in calculations for accurate results.
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On a frictionless horizontal air table, puck A (with mass 0.253 kg) is moving toward puck B (with mass 0.373 kg), which is initially at rest. After the collision, puck A has velocity 0.124 m/s to the left, and puck B has velocity 0.650 m/s to the right.

Calculate DeltaK, the change in the total kinetic energy of the system that occurs during the collision.

- I got ΔK = .007 but was not right
-puck A with speed 0.834 is 0.5*0.253*(0.834)2 . Total energy of the two pucks afterwards are 0.5*0.253*(0.124)2 +0.5*0.373*(0.650)2
 
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What you did should be right, but your change should be negative though.
 
yea...-0.007 was my first answer which was wrong also.

edit...i think it is wrong because it is supposed to be in J.
 
That is in joules. Is this a web assignment? Perhaps you don't have enough significant figures.
 
yea i realized it is in joules after looking again. At first I put in -.007 yesterday and now I put in -0.007 and it says:
"Not quite. Check through your calculations; you may have made a rounding error or used the wrong number of significant figures." which 4 sig figures is right. so I am not sure and usually if I am around the answer it will round it for me.
 
Yeah, you didn't use enough significant figures. Your answer has one sig-fig when your given values have three.
 
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