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Newtons cradle... 
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#1
Jan2211, 09:12 AM

P: 219

assuming collisions are elastic...
right 5 equal masses, if you displace the first ball then you observe balls 24 stationary and 5 moves off with equal speed to the right, as all the momentum and energy is passed to ball 2, ball 1 stops, ball 2 then passes all its momentum and energy to ball 3 and then stops etc... This conserves momentum and k.e. However, if balls 2 and 5 are glued together, and you displace ball 1 with velocity 'u', then the other 4 must move of withspped 4/u to conseve momentum as mu = 4m*u/4, but then kinetic energy is not conserved...? thankssss ! 


#2
Jan2211, 09:36 AM

Mentor
P: 41,323




#3
Jan2211, 11:51 AM

P: 1,135

Doc Al is right
in case I, ball 1 stops as both ball 1.2 has same mass but now its different case, ball 1 collides with mass 4m, so it will now recoil!!!with somewhat lesser velocity than u. 


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