question_answer

Three blocks A, B and C of masses 4 kg, 2 kg and 1 kg respectively, are in contact on a motionless surface, as shown. If a force of 14 N is applied on the 4 kg block then the contact force between A

A) 6 N

B) 8 N

C) 18 N

D) 2 N

Correct Answer: A

Solution :

[a] Acceleration of system \[a=\frac{{{F}_{net}}}{{{M}_{total}}}\] \[=\frac{14}{4+2+1}=\frac{14}{7}=2\text{ m/}{{\text{s}}^{2}}\] The contact force between A and B \[=\left( {{m}_{B}}+{{m}_{C}} \right)\times a=\left( 2+1 \right)\times 2=6\text{ N}\]