Two batteries, one of emf 18V and internal resistance `2Omega` and the other of emf 12 and internal resistance `1Omega` , are connected as shown. The voltmeter V will record a reading of

Options

A. `2.5 R`
B. `4.5R`
C. `7.5R`
D. `1.5R`

Answer

C

Explanation

Initial position

Just before collision
For this system, position fo centre of mass remains same
`[:. Vec(F)_("system") = 0]`
`(M(0) + 5M(12R))/(M + 5M) = (M(d) + 5M (d + 3R))/(M + 5M) rArr d = 7.5 R`