Question

A point charge of mass $m=$ 20 g and charge $q=3\mu C$ is rigidly attached to a non conducting block of mass $M=180$ g which is placed on rough surface with friction coefficient $\mu =0.75$ as shown in figure. Minimum magnitude of electric field required so that the block starts moving :$(g=10m/s^2)$

• A. $2\times {10}^{6}N/C$
• B. $4\times {10}^{4}N/C$
• C. $200N/C$
• D. $4\times {10}^{5}N/C$

Answer 1

Answer: (D)

$4\times {10}^{5}N/C$

Here,
$\theta =ta{n}^{-1}\mu$

$F_{min}=\frac{\mu (m+M)g}{\sqrt{1+{\mu }^2}}=qE$

$E_{min}=\frac{\mu (m+M)g}{q\sqrt{1+{\mu }^2}}$

$=\frac{0.75(0.02+0.180)10}{1.6\times {10}^{-19}\sqrt{1+{0.75}^2}}$

$=4\times {10}^{5}N/C$