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2.On a particular railway,a train driverapplies the brake of

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2.On a particular railway,a train driverapplies the brake of the train at a yellow signal,a distance of 1.0km from ared signal,where it stops.The maximum deceleration of the train is 0.2ms–2.
Assuming uniform deceleration,what is themaximum safe speed of the train at the yellow signal?
A.20m/s
B.40m/s
C.200m/s
D.400m/s
E.100m/s
A
题目说看到信号后要在1km之内停下,火车的最大加速度为0.2m/s^2,问火车的安全速度是多少
v^2=2as=2*0.2*1000(m/s)^2=400(m/s)^2
v=20m/s