Question

Four persons $P, Q, R$ and $S$ are initially at the four corners of a square of side $d$. Each person now moves with a constant speed $v$ in such a way that $P$ always moves directly towards $Q, Q$ towards $R, R$ towards $S$, and $S$ towards $P$. The four persons will meet after time

• A. $\frac{d}{2 v}$
• B. $\frac{d}{v}$
• C. $\frac{3 d}{2 v}$
• D. They will never meet

Answer 1

Answer: (B)

$T=\frac{d}{v_{r e l}}$
$v_{rel} =v-v \cos 90^{\circ}$
$=v-0$
$=v$
$T=\frac{d}{v}$