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Mastering Physics Question? Help?
Determine the stopping distances for an automobile going a constant initial speed of 94 km/h and human reaction time of 0.30 s , for an acceleration a=−3.6m/s^2.
Express your answer using two significant figures.
D= ________ m
Determine the stopping distances for an automobile going a constant initial speed of 94 km/h and human reaction time of 0.30 s, for an acceleration a=−5.8m/s^2.
D=_________ m
Please help! Thanks in advance!
3 Answers
- ?Lv 76 years agoFavorite Answer
First we need to be using consistent units...
94km/h(1000m/km)(3600s/h)=235m/9s
a=-3.6 integrating we get
v=-3.6t+235/9 the time it takes to stop is found when v=0
3.6t=235/9, t=235/32.4, t=1175/162
and then we must add the distance covered during the reaction time to integrating v
d=-1.8t^2+235t/9+.3(235/9) and from earlier t=1175/162 so
d=100m (to two significant figures)
...
a=-5.8
v=-5.8t+235/9 v=0 when t=235/52.2, t=1175/261
d=.3(235/9)+235t/9-2.9t^2
d=67m (to two significant figures)
- Andrew SmithLv 76 years ago
In the very same question you have used m/s^2 and yet km/hr
So you KNOW that before asking a question you must either turn km/hr into m/s or convert the acceleration.
You cannot even START a question where the units are incompatible.
You know that s = ut + 1/2 at^2
so once you have converted the value it is a simple substitution onto a calculator.
