Q143 / 155 · WBJEE 2017 · Physics
Two particles $A$ and $B$ (both initially at rest) start moving towards each other under a mutual force of attraction. At the instant, when the speed of $A$ is $v$ and the speed of $B$ is $2 v$, the speed of the centre of mass is
- Correct answerAzero
- B$v$
- C$\frac{3 v}{2}$
- D$-\frac{3 v}{2}$
Solution
In the absence of external force the speed
$$
u_{\mathrm{co}}=0
$$
$F_{ext}=0$ then
$$
v_{\mathrm{cm} .}=0 \text { always }
$$
Hence, the correct answer is option: 'A'.