Question

Two objects, each of mass 1.5 kg, are moving in the same straight line but in opposite directions. The velocity of each object is $2.5m{s}^{-1}$ before the collision during which they stick together. What will be the velocity of the combined object after collision?

• A. 0 m/s
• B. 3.75 m/s
• C. 0.75 m/s
• D. 3 m/s

Answer 1

Answer: (A)

0 m/s

Let the objects be A and B moving from opposite directions in the same straight line.
$\therefore$ Initial momentum of A $=m\times v$
$=1.5\times 2.5=3.75kgm{s}^{-1}$
Also, initial momentum of B
$=m\times v=1.5\times (-2.5)=-3.75kgm{s}^{-1}$
If v is the velocity of the objects after collision, then final momentum after collision $=3\times v$
Using the law of conservation of momentum, final momentum of A and B $=$
initial momentum of A + initial momentum of B
or $3\times v=3.75-3.75$
or $3\times v=0$ or $v=0$