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2015-05-22T12:22:43+05:30

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M g = T1
F   =  T2  Sine   Theta

T1 =  T2  Cosine   theta  = M g

T2 = Mg / cos theta = F / Sin theta
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Zero Newtons  as in the freely falling state, floor and the man feel weightless. 

Normal reaction from the floor of the elevator is zero…   as   mg – N = m a ;;
as    a = g
   => N = 0


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M = 120 kg            u = 108 km/hr             t = 10 sec.              v = 0

Force is the rate of change of momentum:  

F = (m v - m u) / t

F = (120 * 0  - 120 * 108) / 10
    = 1296 Newtons


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Average resistance is the resistance force like restoration force in a spring.  There is a constant deceleration of the knife when it penetrates into the floor.


   Velocity of the edge of the knife   =  v
   v^2 = u^2 + 2  g h = + 2 g h
   v = sqroot(2 g h)
   Deceleration of the edge of knife in to the floor:    a

   v^2 = u^2 + 2 a s
   a = (0  -  2g h) / 2 s
       =>    a  =  g h / s

2 5 2