A police officer investigating an accident estimates from the damage done that a car hit a stationary car at 25 km/h. If the moving car left skid marks 47 m long, and if the coefficient of kinetic friction is 0.71, what was the initial speed of the moving car?
2006-11-16 11:03:24 · 2 answers · asked by Thomas V 1 in Science & Mathematics ➔ Physics
The friction is Ff = Uk*m*g = 0.71*m*g.
The car had original kinetic energy KEo of (1/2)*m*v^2. At 25 km/h, the car had KE25 of (1/2)*m*(25 km/h)^2. Convert to m/s before squaring. Find an expression for delta kinetic energy that the brakes scrubbed off before impact.
The friction had to do work equal to the delta kinetic energy to bring the car down to 25 km/h. Work is force*distance so
W = Ff*d = 0.71*m*g*47 m
and work is also is equal to delta KE
Set them equal and solve for v.
2006-11-16 12:31:02 · answer #1 · answered by sojsail 7 · 0⤊ 0⤋
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2006-11-16 11:04:16 · answer #2 · answered by Anderwood 2 · 0⤊ 0⤋