Momentum Webquest By: Sara, Shane, Alexa

[Guest strawberry]

Car Crash Web quest write-up

In the car crash web-quest, we were given a situation of an accident. The Cadillac crashed into a non-moving Subaru. We were given only the mass of the 2 cars the distance and acceleration they traveled after they collided. The mass of the Cadillac is 3000kg, and traveled 2 meters with acceleration of -2m/s. The Subaru is 2000kg and went 24 meters with acceleration of -3m/s. To find the velocity of the SUV immediately following the collision, we used the formula Vf^2=Vi^2 + 2AD. We used this because we had the final velocity (zero, because it stopped), the distance, and acceleration. We rearranged it to be equal to vi. Vi^2=vf^2-2AD. After that, we took the square root of our answer, which gave us 2.83m/s velocity of the SUV immediately following the collision. We also needed to do the same thing for the Subaru. We used the same equation arrangement, but this time we used the Subaru’s acceleration (-3m/s) and distance traveled (24m). Our answer came out to be 12 m/s velocity immediately after the collision for the Subaru. Next, we had to find the momentum of both cars immediately following the collision. Using the equation P=MV, we solved it. For the escalade, the mass is 3000m/s, and velocity is 2.83 m/s (answer from last problem). This gave us a momentum of 8490 NS immediately following the collision. For the Subaru, we used the same P=MV equation. Mass is 2000kg and the velocity is 12m/s. The momentum is 24,000NS. To find the momentum of the Cadillac immediately before the collision, we have to add the momentum of the Subaru and Cadillac after the collision. We do this because momentum is always conserved. So, before the collision, the Cadillac had a momentum of 32490. Since the Subaru was not moving, it’s momentum before the collision is zero. The speed of the Subaru before the collision was zero since it was not moving. To find the speed of the Cadillac before the collision, we had to set up a momentum table! The momentum (before) of the Cadillac was 3000kg (vi), since vi is what we were solving for. The momentum (before) of the Subaru was zero, since it was still. The total momentum before was 3000vi. The momentum before of the Cadillac was 8490 and was 24,000 in the Subaru. The total momentum before was 32490. So, 3000vi=32490. Dividing each side by 3000, we got the initial velocity of the Cadillac to be 10.83m/s. since the speed limit was 35 km/hr, we had to convert the Cadillac’s velocity from meters per second to kilometers per hour. After we converted it, we got a speed of 38.988 km/hr. So, yes; the Cadillac was speeding down the road before the collision.