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    susus's Avatar
    susus Posts: 138, Reputation: 2
    Junior Member
    		  
    #1

    Dec 17, 2010, 08:53 AM
    Superman Stopping a train
    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..
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #2

    Dec 17, 2010, 09:40 AM

    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?
    susus's Avatar
    susus Posts: 138, Reputation: 2
    Junior Member
    		  
    #3

    Dec 17, 2010, 10:08 AM
    Comment on ebaines's post
    I guess I did not get the a right ?
    how I can get it ?
    I tried
    f=ma
    0.42/75 =a ?
    ebaines's Avatar
    ebaines Posts: 12,131, Reputation: 1307
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    #4

    Dec 17, 2010, 10:35 AM

    You must have had a value for acceleration in order to solve question 2, right? It's -0.42 x g
    susus's Avatar
    susus Posts: 138, Reputation: 2
    Junior Member
    		  
    #5

    Dec 17, 2010, 11:40 AM
    Comment on ebaines's post
    Huh , I put 0.42 without -
    ! Thanks :)
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