Question

Two small and charged blocks of masses $m_1=m_2=20$ g and charge $q_1=0.6\mu Cand{q}_2=2.4\mu C$ are placed at a distance $r=60$ cm. Coefficient of friction between block 2 and ground is $\mu =0.5$. Find frictional force between block 2 and ground (assuming initially block 2 is at rest).

• A. 0.036 N
• B. 0.36 N
• C. 0.1 N
• D. 1 N

Answer 1

The correct option is A 0.036 N

$F^{}=\frac{k{q}_1{q}_2}{r^2}$
$f_{max}=\mu mg$
$F=\frac{9\times {10}^9\times 0.6\times {10}^{-6}\times 2.4\times {10}^{-6}}{36\times {10}^{-4}\times {10}^2}=36\times {10}^{-3}N{f}_{max}=0.5\times 20\times {10}^{-3}\times 10={10}^{-1}N$
$f_{max}$ is less than F. So friction is equal to $F=0.036N$