An accident occurred when the driver of an automobile traveling down an 8% grade (slope) hit a parked car. A photograph of the accident scene revealed skid marks leading directly to the parked car. Fortunately, no one was injured by this rear end collision. The police officers responding to the call took a statement from the driver, measured the length of the skid marks, and performed a number of skid tests at the accident site. In their final report, the officers reported that the skid marks were 30 m long, that the coefficient of friction was 0.45, and that the driver recalled slamming on her breaks and sliding into the parked car. A footnote in the report indicates that the skid tests were performed over the first 6 m of the skid marks. You must decide, based on the evidence, whether the driver should be given a ticket for exceeding the 25 mph speed limit in the school zone where the accident occurred. If convicted, the driver will also receive 3 points against her driving record. Having already accumulated 4 points against her record in previous violations, the driver immediately hires an investigator to challenge any incriminating evidence. The investigator arrives on the scene before the cars are towed.

(a) Assume that the car is a point mass and draw a free body diagram showing all the forces acting on it as it slides down the hill. (thats a bit hard to show on here but I did the free body diagram already)

( The police made the assumption that the coefficient of friction over the first 6 m was the same as that of the rest of the skid marks. Using this assumption, calculate the acceleration of the car.

© Assume an initial velocity of 25 mph, how far would the car have traveled before stopping?

(d) If the case goes to court, the judge would want to know the minimum velocity of the car before the driver applied the breaks. Calculate the minimum initial velocity of the car.

(e) Based on the evidence in the accident report and the assumptions used by the police, do you recommend to the police charge the person with speeding?




I have been trying to figure out where to even start wi th this question for a few hours now, I would appreciate any help that would guide me in the right direction to possibly solving this.

Thanks

Hi Guys

I guess the Skid marks are assumed to be via the break and not the accelerator.
(a quick look at the parked car should confirm this).

Cheers
Iseason

(sorry, that's the limit of my mathematical genius...lol)