Two bodies A and B of masses 5 kg and 10 kg in contact with each other rest on a table against a rigid wall as shown in fig. The coefficient of friction between the bodies and the table is 0.15. A force 200 N is applied horizontally to A. What are
(a) the reaction of the partition
(b) the action-reaction forces between A and B ?
(c) What happens when the wall is removed? Does the answer to (b) change, when the bodies are in motion? Ignore the difference between `mu_(s)` and `mu_(k)`

Explanation

(a) If be the maximum frictional force acting on the combination of A and B then
`f = mu R = mu(M_(A)+M_(b))g=0.15 (5+10)xx9.8=22.05N`
Reaction of the wall `= F-f=200-22.05 = 177.95 N`
(b) Force exerted by A on
`B = 200 - f_(A)=200 - 7.35 = 192.65 N`
When the partition is removed the masses move together with an acceleration.
`a = ("Net force")/("total mass")=(F-f)/(M_(A)+M_(b))=(177.95)/(15)=11.86 ms^(-2)`
Yes, answer to (b) changes. When the bodies are in motion the force exerted by A on B is given by
`F_(BA)=(F-mu M_(A)g)`- (force required to produce an acceleration)
`= (200-7.35)-(5xx11.86)=133.5 N`.