Question

Two block A and B placed on a plane surface as shown in the figure. The mass of block A is 100 kg and that of block B is 200 kg. Block A is tied to a stand and block B is pulled by a force F. If the coefficient of friction between the surfaces of A and B is 0.2 and the coefficient of friction between B and the plane is 0.3. then for the motion of B the minimum value of F will be:

• A. 1050 N
• B. 700 N
• C. 900 N
• D. 1100 N

Answer 1

Answer: (D)

$f_1=({\mu }_S{)}_A{m}_{A}g$ and $f_2=\left({\mu }_S{)}_B\right(m_A+m_B)g$
The minimum value of F should be (for just tending to move)
$F=f_1+f_2=0.2\times 100+0.3\times 300=110g=1100N$