Question

Two cars A and B start from a point at same time along straight line and their positions are given by $X_A=2t^2-3t$ and $X_B=t^2+2t$. Find the time when relative velocity between A and B becomes zero.

• A. $2s$
• B. $3s$
• C. $3.5s$
• D. $2.5s$

Answer 1

The correct option is D $2.5s$

$X_A=2t^2-3t$
$\underset{–}{X_B}=t^2+2t$
$X_A-X_B=t^2-5t$
Diff w.r.t time
$\frac{d}{dt}(X_A-X_B)=V_A-V_B=2t-5$
$V_{rel}=2t-5=0$
$t=2.5s$