Question

Block A of weight 100 kg rests on a block B and is tied with a horizontal string to the wall at C. Block B weights 200 kg . The coefficients of friction between A and B is 0.25 and between B and surface is 1/3. The horizontal force F necessary to move the block B should be $(g=10m/s^2)$

• A. 1150 N
• B. 1250 N
• C. 1300 N
• D. 1420 N

Answer 1

The correct option is B 1250 N

Required force must be at least equal to friction for offerd by both the contact surfaces.Thai is friction force applied by block B on A and by the ground surface on the block B.
$F={\mu }_{AB}{R}_A+{\mu }_{BS}{R}_B$
$=0.25\times 100g+\frac{1}{3}(100+200)g$
$=25g+100g=125g$
$=125\times 10=1250g$