Question:
Consider the situation shown in figure. Suppose a small electric field Eexists in the space in the vertically upward direction and the upper block carries a positive charge $\mathrm{Q}$ on its top surface. The friction coefficient between the two blocks is $g$ but the floor is smooth. What maximum horizontal force Fcan be applied without disturbing the equilibrium?
[Hint: The force on a charge $Q$ by the electric field $E$ is $F=Q E$ in the direction of $E$.]
Solution:
