Question

Two blocks `A & B` attached to each other by a mass-less spring, are kept on a rough horizontal surface `mu=0.1`. A constant force `F=200 N` is applied on blcok `B` horizon tally as shown below. If a some instant the acceleration of `10 kg` mass is `12 m//s^(2)`, then the acceleration of `20 kg` mass is

A. `2.5 m//s^(2) or 15.5 m//s^(2)`
B. `4 m//s^(2) or 10 m//s^(2)`
C. `3.6 m//s^(2) or 4.1 m//s^(2)`
D. `1.2 m//s^(2) or 1.3 m//s^(2)`

Answer 1

Correct Answer - A
(i) Let the spring is in a elongated state.

`f_(A)=0.1xx10g=10N` and
`f_(B)= -1xx20g= 20N`
`kx-10=10xx12rArrkx=130N`
`200-kx-20=20(a_(B))rArra_(B)=2.5m//s^(2)`

(ii) Let the spring is in a compressed state.
`kx-10=10xx12rArrkx=130N`
`200+kx-20=20(a_(B))rArra_(B)=15.5m//s^(2)`