Chap 15. 3 Problem 15- 51

[@matthewspence7476]

Hold on a minute, in your calculations you inexplicably change the mass of car B from 15x10^3 kg to 10x10^3 kg. Why did you do this? The mass can't just change like this? The key got the same answer so I am very confused

[@Raed.Merhi.]

well im sure he's following the key, and im sure he passively just followed it without really questioning such detail. its just a mistake dont take small things like this too seriously just follow what makes more sense and whats closer to logic or else youre gonna have a hard time following dont get too stuck on the silly mistakes of others but rather see the bigger picture, yet focus on your silly mistakes cause those might actually lose you marks( partials or complete ones if the instructor of your course was too rude and technical) or might be conceptual mistakes which has its consequences too on your performance.

[@Justinian-e6s]

He did it wrong, he was supposed to do 15 * 10^-3 but the velocity of B is not positive its -2.78 and if you follow that logic you end up getting V = 2.78m/s which you can use later to the final equation to get delta S

[@Raed.Merhi.]

why did is the momentum of car B considered +ve when the principle of LI&M was applied, is it because it is considered internal in the system we considered, or is momentum absolute, im just lost why both momentums are positive yet the cars are moving towards each other( in opp directions) does it not depend on the direction since both are in the same system

[@thegamingmonster4252]

Same question. Have you found the reason for that +ve sign yet?

[@roseannsotto3381]

@@thegamingmonster4252 if you plug it in the calc and follow the negative sign, you'll get the same answer which is 2.78m/s