A pedestrian was struck crossing a dry concrete road. The skid distance of the F

Question

A pedestrian was struck crossing a dry concrete road. The skid distance of the Ford Explorer was measured to be 62 feet.  If the pedestrian was hit halfway along the skid path, what was the impact velocity of the car?  Usually, impacting a pedestrian does not significantly alter the speed of a typical vehicle

A pedestrian was struck crossing a dry concrete road. The skid distance of the Ford Explorer was measured to be 62 feet. If the pedestrian was hit halfway along the skid path, what was the impact velocity of the car? Usually, impacting a pedestrian does not significantly alter the speed of a typical vehicle - discuss if your think that this is a reasonable (or unreasonable) assumption.

Explanation / Answer

Fric coeff = 0.7

Friction force = 0.7*mg

Work done by Fric force = (0.7*mg)*(62/2) = 21.7*mg

1/2*mv^2 = 21.7*mg

v = sqrt (2*21.7*g)

= sqrt (2*21.7*32.2)

= 37.38 ft/s

= 25.5 miles/hr

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