Help me in understanding and solving

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A child pulls a train of 2 cars with a horizontal force F of 10N .
Car1 has a mass of m1=3kg, and car2 has a mass of 1kg
The mass of the string connecting the the cars is small enough to be set equal to zero, and the friction can be neglected .


a- Find the normal force exerted on each car by the floor.
b- What is the tension force in the string
c- Find the acceleration of the train




thanx



well please help me to solve and understand this problem
I can't figure out why the normal force in this problem is equal to the weight or how to find the acceleration.! b]
 
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This is the way i did it

a- Car 1
N-F= ma
N - mg = ma
N= mg+ma
N= 3*9.8 + 3*9.8 = 29.4 + 29.4 =58.8

Car 2
The same way so its N =19.6

b- F-T = m a
F= mg= 3+1 * 9.8 = 39.2
so
39.2 - T = 1+3 * a
-T = -39.2 +4*a
a=?
I COULDN'T FIGURE OUT HOW TO FIND THE ACCELERATION.!

PLZ PLZ PLZ HELP ME UNDERSTANT THIS PROBLEM
I'VE AN EXAM IN 2 DAYS ANT I CAN'T UNDERSTAND A WORD OF THIS SUBJECT
 
goto this page
100% correct
http://knowhowstuff.blogspot.com/2009/05/physics-forum-answers.html"
 
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