Posted by Sarah on Friday, October 11, 2013 at 2:36am.
I really don't get why I am getting this question wrong? Please can you explain to me how to do this question step by step so that I can understand it please? :( i have been stuck on this question for quite a while now.
Determine the stopping distances for an automobile with an initial speed of 89 km/h and human reaction time of 2.0 s for the following:
(a) an acceleration a = 4.0 m/s2.
(b) a = 8.0 m/s2.

Physics  Henry, Saturday, October 12, 2013 at 10:12pm
Vo=85000m/h = 85000m/3600s = 23.61 m/s.
a. V = Vo + a*t
T = (VVo)/a + Tr
T = (023.61)/4 + 2s = 7.9 s = Stopping time.
d = Vo*t + 0.5a*t^2
d = 23.61*7.9 + 0.5*4*7.9^2 = 61.7m
b. T = (023.61)/8 + 2s = 4.95 s.
d=23.61*4.95 + 0.5*(8)*4.95^2=18.86 m.

Physics  Henry, Saturday, October 12, 2013 at 10:44pm
CORRECTION:
Vo=89,000m/1h = 89000/3600s = 24.72 m/s
a. V = Vo + va*t
T = (VV0)/a + Tr
T = (024.72)/4 + 2s.=8.18 s.=Stopping
time.
d = Vo*t + 0.5a*t^2
d=24.72*8.18 + 0.5*(40*8.18*2=68.38 m.
b. T = (024.72)/8 + 2s = 5.09 s.
d=24.72*5.09 + 0.5*(8)*5.09^2= 22.19 m.
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