Question

A particle starts from rest with uniform acceleration a. Its velocity after n seconds is v. The displacement of the particle in the last two seconds is :
(A)2v(n-1)/n
(B) V(n-1)/n
(C) V(n+1)/n
(D) 2v(2n+1)/n

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Answer 1

Answer:

$\textcolor{red}{\mathrm{A)}} 2v(n-1)/n$

Explanation:

After n seconds, velocity is v=an.

After (n-2) seconds, velocity is a(n-2).

Thus, using the formula:

s=ut+(1/2)at², we have in the last two seconds; t=2, u=a(n-2)

Hence, s= 2a(n-2)+(1/2)a(2)²

Solving this, we have s= 2an-2a.

Now put v=an, that is, a=v/n, to get the answer.