Question

A body is travelling towards East with a speed of $9\, m / s$ and with an acceleration of $2\, m / s ^{2}$ acting along West on it. The displacement of the body during the $5^{\text {th }}$ second of its motion is

• A. 0.25 m
• B. 0.5 m
• C. 0.75 m
• D. zero

Answer 1

Answer: (D)

zero

Answer 2

Displacement in the nth second is given by
$S_{n}=4+\frac{a}{2}(2 n-1)$
In this problem retardation is involved.
Thus, the equation becomes
$S_{n}=4-\frac{a}{2}(2 n-1)$
Given $u=9\, m / s , a=2\, m / s$
$n=5$
$\Rightarrow S_{5}=9-\frac{2}{2}(2 \times 5-1)$
$=9-9=0$