A 1600 kg car traveling at 18.9 m/s to the south collides with a 4200 kg truck that is initially at rest at a stoplight. The car and truck stick together and move together after the collision. What is the final velocity of the two-vehicle mass? Answer in units of m/s. Seemingly incredibly simple physics problem, but I keep getting it wrong. Perfectly inelastic collision, therefore formula = m1v1+m2v2=(m1+m2)vf 1600*18.9+4200*0=(1600+4200)vf 30240=(5800)vf 30240/5800=vf vf = 5.213793103 m/s Yet, when I submit this answer the website keeps telling me I'm wrong. I'm pretty sure I'm doing this right...
Sometimes websites make you get the right number of sig figs in your anwser so i guess you can try to cut the decimal places to 3 or 4 and round then try that answer... i already forgot the correct number of sig figs in the problem but its prolly closer to 3 or 4 than it is to 8 decimal places like you have.
That's not the problem. The website we use to submit problems doesn't factor in sig figs. So there's either more to this problem than I originally had thought or the website is trying to fail me.
Looks good...sometimes those sites like Pearson and such have rounding issues...hell sometimes they've been plain wrong. It's frustrating, but hey, in the end it helps you learn even more. (consolation prize)
If you watched The Big Bang Theory every week like you're supposed to, you wouldn't have had to waste our time with this silly question.
Inelastic collisions are a pretty simple problem but the way the question was set up is definitely frustrating. The assumption is made in the problem that in the y-axis, North is Positive and South is Negative. I looked at it the same way as you did where the first object listed is moving in the positive direction where the second object if opposing would be in the negative direction. Physics is good stuff, outside of static equilibrium which to this day I still don't understand. Anywhoo, if the remarks of the fellow bbs posters in response to your question are any indication of their level of intelligence, you should be feeling pretty good about yourself right now -BV
Notwithstanding that you already have the answer, itself a bull**** issue of question wording, I hate these types of questions. I liked physics, but don't feel like these types of questions encourage students to enjoy the field. Um, what about friction, road surface, wind speed, all sorts of other factors which should impact combined velocity?
