Two bodies having same mass 40 kg are mov

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Two bodies having same mass $40\, kg$ are moving in opposite directions, one with a velocity of $10$$m/s$ and the other with $7\,m/s.$ If they collide and move as one body, the velocity of the combination is ........ $m/s$

A

$10$

B

$7$

C

$3$

D

$1.5$

Two bodies having same mass $40\, kg$ are moving in opposite directions, one with a velocity of $10$$m/s$ and the other with $7\,m/s.$ If they collide and move as one body, the velocity of the combination is ........ $m/s$

By the conservation of momentum
$40 \times 10 + (40) \times ( - 7) = 80 \times v$ ==> $v = 1.5\,m/s$