# Two particles having position vectors $\overrightarrow {r_1}= (3 \hat i - 5 \hat j)m$ and $\overrightarrow {r_1}= (-5 \hat i +3 \hat j)m$ are moving with velocities $\overrightarrow {V_1}= (-4 \hat i +3 \hat j)m/s$ and $\overrightarrow {V_2}= (-a \hat i +7 \hat j)m/s$. If the collide after 2 seconds, the value of a is

$\begin {array} {1 1} (a)\;2 & \quad (b)\;4 \\ (c)\;6 & \quad (d)\;8 \end {array}$

## 1 Answer

$\bar {r_2}-\bar {r_1}=-8 \hat {i}+ \hat {j}$
$\bar {V_2}- \bar {V_1}=(-a+4) \hat i + 4 \hat j$
$X\; disp= -8$
$(-a +4)2=-8$
$-a+4=-4$
$a=8$
answered Nov 23, 2013 by

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