What is the final speed of the truck and car after an elastic collision?

AI Thread Summary
In an elastic collision scenario, a 750-kg car is rear-ended by a 1790-kg truck traveling at 16.0 m/s. The calculations for the final speeds of both vehicles involve using conservation of momentum and kinetic energy equations. Initial attempts yielded incorrect results, prompting a reevaluation of the method used. The correct final speeds were determined to be approximately 6.56 m/s for the truck and 21.51 m/s for the car after adjusting the calculations. The discussion highlights the importance of accurately applying the principles of physics in collision problems.
godkills
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A 750- kg car stopped at an intersection is rear-ended by a 1790- kg truck moving with a speed of 16.0 m/s

If the car was in neutral and its brakes were off, so that the collision is approximately elastic, find the final speed of the truck.

Find the final speed of the car.


256 = (28640 -750v2)2 / 17902 + .42v22

v2 = 22.51
v1 = 6.757

i don't know what am i doing wrong but i get wrong answer.
 
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I can't really understand what you have done. Explain it...
 
1790kg x 16 m/s = 1790s1 + 750 s2 where s1 and s2 is velocity of truck and car after collision.

s1=(28640 -750s2)/1790

1/2(1790)(16)^2=1/2(1790)(s1)^2 +1/2(750)(s2)^2

196=s1^2+0.42s2^2 equation number 2

then i plugged in s1 into equation number 2
 
The method is fine, there must be a problem in calculation. If you want to ease the calculations then use coefficient of restitution.
 
s2=21.51
s1=6.56

new ones still wrong i seriously don't know why i performed the calculations correctly
 

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