On a test track, an SUV of mass 2000 kg traveling at 12 m/s hits a stationary ca
ID: 2010290 • Letter: O
Question
On a test track, an SUV of mass 2000 kg traveling at 12 m/s hits a stationary car of mass 1000 kg. the car crumples and stays in contact with the SUV, they move together as a unit.A. Without calculations, which vehicle undergoes a greater change in velocity during the collision? how do you know?
B. Without calculations, if you can intuitively guess the post collision speed of the two vehicles, what would it be?
C. Calcualate the post collision speed using momentum.
D. if you got stuck in part B, do you see a way that you could have guessed the post collision speed?
Explanation / Answer
Since the first part is with no calculations let's do some reasoning. If a HUGE train hit a stationary car, which one would experience the greatest change in velocity?... A train will hardly even notice the car in it's path. The same idea here, the SUV slows down a little and the stationary car speeds up quickly.
Post collision speeds... it has to be less than 12 m/s right? The SUV will definitely slow down after the collision. The SUV weighs 2000kg which is twice that of the car so I would say the SUV slows down to 2/3 of it's original velocity. So, 8 m/s
p=mv momentum=mass x velocity
(mass of SUV)(starting velocity of SUV) +(mass of car)(starting velocity of car) = (mass of SUV and car together)(final velocity of wrecked vehicles)
(2000kg)(12m/s) + (1000kg)(0m/s) = (3000kg)(v)
solving for v gives 8m/s