A cubical block of side a and of mass `m` rests on a rough horizontal surface. A horizontal force `F` is applied to normal to one of the faces at height `h` above the base `hgta//2`. What is the minimum value of `F` for which the cube begins to tip about an edge?

Explanation

In the absence of any external force the normal contact force passes through the center of mass. When the external force is applied, normal contact force shifts in the direction of the applied force to counteract the deflecting torque due to the applied force. At the instant of tipping over about the edge the normal contact force passes through the edge. If it is not able to counter to deflecting torque, toppling takes place.
The cube will tip about `A` if the deflecting torque due to `Fge` the restoring torque due to `mg`
`Fhgemg.(a)/(2)`
`Fge(mga)/(2h)`
`F_(min)=(mga)/(2h)`