An insect crawls up a hemispherical surface very slowly. The coefficient of friction between the insect and the surface is $1/3$. If the line joining the centre of the hemispherical surface to the insect makes an angle $\alpha $ with the vertical, the maximum possible value of $\alpha $ so that the insect does not slip is given by
$\cot \,\alpha = 3$
$\sec \,\alpha = 3$
$\cos ec \,\alpha = 3$
$\cos \,\alpha = 3$
A block is placed on a rough horizontal plane. A time dependent horizontal force $F = Kt$ acts on the block. Here $K$ is a positive constant. Acceleration-time graph of the block is
A block $B$ is pushed momentarily along a horizontal surface with an initial velocity $V.$ If $\mu $ is the coefficient of sliding friction between $B$ and the surface, block $B$ will come to rest after a time
A block of weight $W$ rests on a horizontal floor with coefficient of static friction $\mu .$ It is desired to make the block move by applying minimum amount of force. The angle $\theta $ from the horizontal at which the force should be applied and magnitude of the force $F$ are respectively.
A heavy box is solid across a rough floor with an initial speed of $4 \,m / s$. It stops moving after $8$ seconds. If the average resisting force of friction is $10 \,N$, the mass of the box (in $kg$ ) is .....
When a body is lying on a rough inclined plane and does not move, the force of friction