Two masses 10 kg and 20kg resplectivley are connected by a massless spring as shown in figure. A force of 200 N acts one the 20 kg mass.At the instant shown is figure the 10 kg mass has acceleration of 12 `m//s^(2)`.The vlalue of acceleration of 20 kg mass is

Explanation

Equation of motion for `m_(1)` is `F=m_(1)a_(1)=10xx12=120N`. Force on 10kg-mass is 120N to the right. As action and reaction are equal and opposite, the reaction force F on 20kg mass F=120N to the left.
`therefore` Equation of motion of `m_(2)` is `200-F=20a_(2)`
`rArr200-120=20a_(2)rArr20 a_(2)=80rArra_(2)=(80)/(20)=4ms^(-2)`