# physics

Running into the train at that speed would severely damage both train and passengers. Calculate the minimum time Superman must take to stop the train, if the passengers experience an average horizontal force of 0.520 their own weight.

and

How far does the train then travel while being slowed to a stop?

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3. 👁 730
1. acceleration = -.520(9.8) = -5.1 m/s^2
initial speed Vo = 65 km/hr(1hr/3600s)(1000 m/km)=18 m/s

From your physics text for constant acceleration
v = Vo + a t
here we have our initial Vo is 18 and we stop, v = 0
0 = 18 - 5.1 t
so t = 18/5.1 = 3.53 seconds

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posted by Damon
2. i have one more

How far does the train then travel while being slowed to a stop?

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posted by erin
3. d = Vo t + (1/2) a t^2
d = 18 * 3.53 - (5.1/2)(3.53)^2

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posted by Damon
4. By the way, if you are really used to these problems you would just use the average speed during deacceleration (18/2 = 9 m/s) times the time (3.53 s)

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posted by Damon

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