A 100 kg car moving rightward at 2 m/s collides elastically with a second car. Both cars end up bouncing off with the same speed (just in the opposite direction) than they had before they collided. What was the mass and speed of the second car? (​Adjust the Blue car mass to 100 kg and its velocity to +2 m/s. Set the bumper to Bouncy. For what value of Red car mass and velocity will the two bounce off without changing speed?)

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Distance covered = speed x timethe distance traveled going against the stream = distance traveled with the stream.therefore it is the speed and the time that are the variables.as he travels the same distance both ways, speed x time is the same for each way.going upstream his speed is 4 kph; going downstream his speed is 6 kph.therefore we have two simultaneous equations: time upstream x 4 = time downstream x 6time upstream + time downstream = 60 minutestherefore we have the equation: time upstream = 6/10 hour, time downstream therefore = 4/10 hour.distance traveled at 4km/hr in 6/10 hour = 24/10 = 2.4km.check: distance traveled at 6km/hr in 4/10 hour = 24/10 = 2.4km.