Concems have been raised about an intersection in your town. Due to the layout o

Question

Concems have been raised about an intersection in your town. Due to the layout of the road, it is only possible to see the stop sign for the intersection when a car is about 300 m rom i, and s0 many hvers are unable to stop in time for it Your goal is to propose a new speed limit for the road since the old speed limit (75 km/h) has lead to too many accidents. Researching various types of tires indicates that the coefficient of static friction between a rolling tire and asphalt is between 0.842 and 0.941, whereas the coefficient of kinetic friction between a skidding tire and asphalt is between 0.550 and 0.754 Considering that you want no drivers who follow the speed limit blowing past the intersection, by how much should the speed limit be lowered (in km/h)? Be sure to give your answer to the proper number of significant figures! Reduce the speed limit by... Number km/h

Explanation / Answer

initial speed= v_i

final speed v_f = 0

distance s = 30 m

frictional force f = uk*m*g

work done by frictional force Wf = fk*s*cos180 = -uk*m*g*s

from work energy relation W = K_f - Ki

-uk*m*g*s = (1/2)*m*(v_f^2 - v_i^2)

v_i = sqrt(2*uk*g*s)

v_i = sqrt(2*0.55*9.8*30)

v_i = 18 m/s = 18*(18/5) km/h

v_i = 64.8 km/h <<<-------answer

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