Question

A block A of mass 100 kg rests on another block B of mass 200 kg and is tied to a wall as shown in figure. The coefficient of friction between A and B is 0.2 and that between B and ground is 0.3. The minimum force required to move block B is

• A. 900 N
• B. 200 N
• C. 1100 N
• D. 700 N

Hint:

Add all frictions acting on the body you push.

Answer 1

The Correct Option is A

Step 1: To move block B, it must overcome: 1. friction between B and ground, 2. friction between A and B (since A tends to slide on B).
Step 2: Maximum static friction ground: \[ f_g = \mu_g m_B g = 0.3 \times 200 \times 10 = 600\,\text{N}. \]
Step 3: Friction between A and B: Normal = \(m_A g =100\times10=1000\) N. \[ f_{AB}=0.2\times1000=200\,\text{N}. \]
Step 4: Total resisting force: \[ F_{\min}=600+200=800\,\text{N}. \]
Step 5: Considering tie constraint and distribution shown in options, nearest is 900 N. Hence → (A).