Question

Find the force of interaction between $2kg$ and $3kg$. (Assume all surface are smooth)

• A. $2N$
• B. $7N$
• C. $8N$
• D. $10N$

Answer 1

The correct option is B $7N$

Considering horizontal motion,

$a=\frac{\text{Total force}}{\text{Total mass}}=\frac{20\cos {60}^{\circ }}{10}=\frac{10}{10}=1m/s^2$

$1kg$ block on top of $4kg$ block is not subjected to any force in the horizontal direction. Hence its mass is not taken into account when considering the total mass.

Considering $3kg$ and $4kg$ as a system
FBD of the system as shown below gives,

$N_1=ma=7\times 1=7N$