Answer:
2.75 N
Explanation:
Given that,
Box A has a mass 21.0 kg and box B has a mass 8.0 kg.
A horizontal force of 100N is exerted on box A.
Let a be the acceleration of the system. Using second law of motion,
[tex]F=(m_A+m_B)a\\\\a=\dfrac{F}{(m_A+m_B)}\\\\a=\dfrac{10}{(21+8)}\\\\a=0.344\ m/s^2[/tex]
Now applying Newton's second law to box B. So,
[tex]F_A=m_Ba\\\\=8\times 0.344\\\\=2.75\ N[/tex]
So, 2.75 N is the force that box A exerts on box B.