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Homework Statement
car is braking evenly. The brakes are in locking essentially (not ABS brakes) Car is sliding under sliding friction. Car comes to a fullstop at the distance of 150m
starting velocity was 100km/h (27,77m/s)
calculate
a) braking time
b)cars deceleration
c) friction coefficient between tyre and road
known variables
s=150m
mass=1500kg
##V_0=27,77 m/s##
##V_1= 0 m/s##
##t_0= 0s##
##t_1= ?##
##a= ?##
## F= ?##
Homework Equations
##V_{avg} * t = s##
##V_1= V_0 +at##
##F=ma##
##F=F_μ##
##a=μ*g##
##F_μ= μ* F_N##
##|F_N|=|G|##
##G=mg##
The Attempt at a Solution
This was an old exam problem the most difficult of them I would say.
I did not do it very well, under the time pressure. But I attempted to do it at home afterwards when I hopefull was able to do better quality creative thinking.
It is known that car decelerates at even acceleration.
therefore (it took me some considerable time to realize how to calculate the braking time, this was tough cookie for me)
##s= V_{avg} * t_1##
##t_1=10.8030s##
thus
##V_1=V_0+at##
##a= -2,5705 m/s^2##
thus
after realizing that F_net upon the car in the horizontal axis should equal the force of braking. Gravity and support force cancel out.
##F_μ=ma##
apparently according to my notes from lecture, it seems that
thusly
##a= μ*(g)##
##-2,5705m/s^2= -9.81m/s^2 *μ##
##μ=0,2620##