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

[godkills]

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.

 

[ashishsinghal]

I can't really understand what you have done. Explain it...

 

[godkills]

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

 

[ashishsinghal]

The method is fine, there must be a problem in calculation. If you want to ease the calculations then use coefficient of restitution.

 

[godkills]

s2=21.51
s1=6.56

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

 

[godkills]

Ah nvm, i found out the method was wrong and so I had to use this one.

http://upload.wikimedia.org/math/a/b/6/ab6645eaf09c6da1ba47b0f662615140.png