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by the graph we see that
after 20 sec, the train will stop, and it doesnt matter if you add an extra 10, the distance wont change.
v0=40m/s
a=-2m/s^2
t=20s
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v=?
x=?
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v=v0-at (- because the acceleration is negetive)
v=40-2*20
v=40-40
v=0 - the speed after 20 sec
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x=x0+v0t-at^2/2
x=40*20-2*20^2/2
x=800-400
x=400
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the train will travelled 400meter within 20 secs, thats why the train travelled the same distance with 30 sec..
hope i helped.
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