please also specify the correct method to solve the question ;

a particle starts from rest with uniform acceleration 'a' . its velocity after n second is u . the displacement of the body in the last 2 second is :

(a)     2v(n-1) / n

(b)     v(n-1) / n

(c)     v(n+1) / n

(d)     2v(2n+1) / n

v = an

 

S_n-2 = a(n-2)²/2

      

S_n = an²/2

 

S_n - S_n-2 = (4n - 4)a/2

             =  2na - 2a

             = 2v - 2v/n

             = 2v (n - 1)/n--------------(a)

 

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Ok

Now v=an

Let the total displacement be S

Now find the total displacement in n-2  seconds which is

S1=1/2 a(n-2)whole square

 

So The total displacement in the last 2 seconds will be

S-S1 = 1/2a(nsquare - (n-2)square)

        =  a(2n-2)---------1

But v=an

Substituting in 1

S-S1=2V(n-1)/n

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