1. The problem statement, all variables and given/known data Car 1 weighing 1000 kg crashes into the rear of parked car 2 weighing 1100 kg and stops. Car2 moves ahead 2 ms^{2}. What is the velocity of car1 at impact? 2. Relevant equations (m1v1+m2v2)=(m1v3+m2v4) 3. The attempt at a solution (m2V4)/m1 (1100*2)/1000 2.2ms^{2}= 2200/1000 Okay, now I know this is right, but what I don't know is how do they arrive at the equation (m2v4)/m1 ????
If you examine your original conservation of momentum equation, let [itex]v_1, v_3[/itex] be the initial and final speeds of car 1, respectively, and let [itex]v_2,v_4[/itex] be the initial and final speeds of car 2, respectively. From the context of the problem, what must be true about speeds [itex]v_2[/itex] and [itex]v_3[/itex]?
So because they have no momentum they cancel out which means you rewrite the equation to solve for velocity1 (1000*2.2+1100*0)=(1000*0+1100*2) (1000)=(1100*2) (m1)=(m2v4) (m2V4)/m1 (1100*2)/1000 2.2ms2= 2200/1000 Is that how it is done?
Yes, that's the idea. Conservation of momentum dictates [itex]m_1 v_1 = m_2 v_4[/itex], solving for the initial speed is just an algebra problem.
Thanks Steely Dan... that wasn't as hard as I thought it would be... mind you that was an easy momentum problem for you, but difficult for me. I imagine it would be harder if you had 1 vehcile t-bone another and they both have pre and post impact velocities.
I was just re reading your posts... ...when I re read this post the light started to flicker. Thanks again Steely Dan