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netrunnr
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Homework Statement
a vehicle starts from rest and accelerates at a reate of 2.0m/s2 in a straight line til it reaches a speed of 20m/s. then it slows to constant 1.0m/s2 til it stops.
how much time elapses from start to stop?
how far does the vehicle go?
Homework Equations
I have:
a1 = 2.0m/s2
a2 = 1.0m/s2
v1 = 2.0m/2
v2 = 0.0m/2
The Attempt at a Solution
what I did was this:
t1=0s then 2m/s2 * 0s= 0
t1=1s then 2m/s2 * 1s = 2m/s
t1=10s then 2m/s2 * 10s = 20m/s
that gives me 10 seconds later the vehicle gets to a = 20m/s
so now the same thing for slowing down setting my 20m/s to t=0 and working from there
t2=0 then 1m/s2 * 0s = 0
t2=1 then 1m/s2 * 1s = 1m/s
t2=20 then 1m/s2 * 20s = 20m/s
now I have:
total time: t2 + t1 = 20s + 10s = 30s
this is the only equation given that I know how to apply:
total distance: based on a = d/t set to solve for d so d = at
total distance: d1 = 2.0m/s * 10s = 20m
d2 = 1.0m/s * 20s = 20m
20m + 20m = 40m
total time traveled is 30s
total distance traveled is 40m
the problem is I did not use any of the basic equations I was given in my book for this. I am at a loss as to how to match my equations to my work... and seeing as this is the first week of the semester I have a feeling this is going to come back to haunt me drastically in about 4 weeks.
thanks for any advice offered.