only the 3rd part...
Superman Stopping a train
1 - Find the speed at which Superman (mass=75.0 kg) must fly into a train (mass = 18511 kg) traveling at 75.0 km/hr to stop it.
(in km/hr) 1.85×104 km/hr

2- Your receipt no. is 161-3854Help: Receipt Previous Tries
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 0.420 their own weight.
(in s) 5.06 s


3- Your receipt no. is 161-2562Help: Receipt Previous Tries
How far does the train then travel while being slowed to a stop?
(in m)

I'm done with 1 and 2.. just 3 left..
I tried to use..
s= s +v(delta T) + 0.5*a( delta T) ^2

I failed..
waiting for help..

For 3, you have the right equation - what did you get for an answer? Are you converting the 75 Km/Hr to m/s? And is your value for a negative?

I guess I did not get the a right ?
how I can get it ?
I tried
f=ma
0.42/75 =a ?

You must have had a value for acceleration in order to solve question 2, right? It's -0.42 x g

Huh , I put 0.42 without -
! Thanks :)