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Forces at Play
Directions - Read the passage below then answer the questions that follow.
While attending Texas A&M, I decided to make a late-night trip back to Dallas in the fall of 1992. I began the drive around midnight, traveling east on TX-21/190 toward Madisonville.
I had just started along TX-21/190 when a dark figure suddenly appeared in the road. I had to make a split-second decision: swerve to try to avoid whatever was in front of me, or brake and hit it.
Swerving at nearly 60 mph likely would have sent me into the culvert along the side of the road. The culverts had several driveways with large concrete drainage pipes running through them. Hitting one of those pipes would have brought my car to an immediate stop.
I made the decision to lean toward the passenger seat, brake, and hit whatever was in the road.
I was briefly knocked unconscious after colliding with the unknown object. When I awoke, my car was stopped crossways in the road, my foot was still on the brake, and I couldn’t see anything. It was pitch black outside, and my glasses had been knocked off my face. Whatever I had hit was nowhere in sight.
I had to decide what to do next. I needed to find somewhere to call for assistance. I considered knocking on the door of one of the homes along the roadside, but decided against it given how late it was and how isolated the area seemed—who knew who or what might answer the door. The only other car I had seen was about a quarter mile behind me before the collision and then about a quarter mile down the road afterward.
Leaving my car in the middle of the highway wasn’t a good option, so I got out and pushed it into the culvert immediately behind where it had come to rest. The rear of the car went in first, leaving the car pitched upward at an angle.
I then searched for my glasses. I found them on the passenger-side floorboard of the car, put them on, and still couldn’t see. The lenses had been knocked out of the frames. After recovering the lenses and popping them back into the frames, I decided to walk back to the gas station at the corner of TX-21/190 and Highway 6.
Before leaving for the gas station, I decided to leave the headlight lights on so I could find my car when I returned with help. The angle of the car was such that the headlights were pointing up and out into the darkness.
When I arrived at the gas station, a Circle K at the time, I called for assistance. An officer arrived, and since I did not require immediate medical attention, he drove me back to my car. I was required to sit in the back seat behind the cage.
During the drive, I explained what had happened. When I couldn’t describe what I had hit, the officer quickly began asking about my sobriety and possible drug use, neither of which had anything to do with the accident.
When we arrived at my car, the officer quickly assessed the situation and determined what I had hit. His evaluation of the large hoof scratch across my hood, horsehair caught in the wiper arms, and the large pile of horse manure in the road led him to say simply, “You hit a horse.”
But where was the horse? It was nowhere in sight.
The officer and I walked the scene looking for it. Eventually we wandered a short distance down the road toward a small building. Along the side of the building stood the horse, clearly in distress. At that point, the officer called for assistance for both my vehicle and the horse. Ironically, the small building was a veterinary clinic—but it was closed.
Soon several vehicles began arriving. I can only assume they had been informed that a car had hit a horse. Each person would walk up to my car and peek inside, expecting to see an injured driver. When I spoke up and said that I was the driver, they all took a step back in surprise.
It took several days to complete the accident paperwork and determine who owned the horse. Fortunately, the owners had insurance, so my medical bills were paid, got new glasses and I received the value of my car, allowing me to buy another Honda CRX.
The horse turned out to belong to the owner’s daughter and was her show horse. The accident report listed the address of the horse’s owner. As it turns out, the culvert where I had pushed my car off the road was directly in front of the horse owner’s house.
In hindsight, not knocking on that door that night turned out to be a pretty good decision.
Questions
Answer the following quesitons. The mass of a Honda CRX is is 825 kg (1819 lbs) and the estimated mass of a show horse is 500 kg (1102 ibs). The initial speed at impact was 20 m/s (approx. 45 mph) at the coefficient of static and kinetic friction are 0.9 and 0.7 respectively.
1. Which experienced the greater force - the horse or the car?
2. Which experienced the greater acceleration - the horse or the car?
3. Which experienced the greater change in momentum - the horse or the car?
4. Which experienced the greater impulse - the horse or the car?
5. Sketch a force vs. time graph for the horse and car.
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