Question

A block A with mass 100 kg is resting on another block B of mass 200 kg. As shown in figure a horizontal rope tied to a wall holds it. The coefficient of friction between A and B is 0.2 while coefficient of friction between B and the ground is 0.3. The minimum required force F to start moving B will be

• A. 900 N
• B. 100 N
• C. 1100 N
• D. 1200 N

Answer 1

Two frictional force will work on block B.

$F = f _ { A B } + f _ { B G }$ $= \mu _ { A B } m _ { a } g + \mu _ { B G } \left( m _ { A } + m _ { B } \right) g$

= 0.2 × 100 × 10 + 0.3 (300) × 10

= 200 + 900 = 1100N. (This is the required minimum force)