A car hits a tree at an estimated speed of 10 mi/hr on a 2% downgrade. If skid marks of 100 ft. are observed on dry pavement (F=0.33) followed by 200 ft. on an unpaved shoulder (F=0.28), what is the initial speed of the vehicle just before the pavement skid was begun?

Explanation:

The deceleration of the car on the dry pavement is found by the Newton's Law:

Where:

Likewise, the deceleration of the car on the unpaved shoulder is:

The speed just before the car entered the unpaved shoulder is:

And, the speed just before the pavement skid was begun is:

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