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TalibanNinja
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Homework Statement
A driver carelessly ignores the reduced speed limit of 40.0 km/h in a school zone and continues at 65 km/h. Assuming a good reaction time of 0.80 s, how many more metres will it take him to stop than if he had reduced his speed? Assume 2000kg car has a constant braking friction of 12000N. (Must use work-energy theorem)
va=11.11m/s
vb=18.05ms
Ff=12000N
m=2000kg
g=9.8m/s^2
Homework Equations
Ff=μFn
Work done to an object = change in kinetic energy
Wf=Ek
μmgd=1/2mv^2
d=v^2/2μg
The Attempt at a Solution
μ=Ff/Fn
μ=12000N/(2000kg*9.8m/s^2)
μ=0.61
da=(11.11m/s)^2/2*(0.61)(9.8m/s^2)
da=10.32m
db=(18.05m/s)^2/2*(0.61)(9.8m.s^2)
db=27.25m
Δd=db-da
Δd=27.25m - 10.32m
Δd=16.93
Therefore it takes the driver 16.93m longer to stop than if he slowed his speed.
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