Please help with this question

Question

The force that causes the acceleration of m₂ is not the applied external force; rather, it is the contact force from m₁. Applying Newton's second law to m₂, what is the magnitude of the contact force, P₁₂

, between the two blocks for the case above?

Answer 1

the total applied force on the m2, treat m2 as separate object and draw FBD

so apply newton 2nd law

F.net = P₁₂=m_2.a