If the overbridge is concave instead of being convex,the thrust on the road at the lowest position will be

What force should be applied on the wedge so that the block over it does not move? (All surfaces are smooth)

$A$ $1 \,kg$ block situated on a rough incline is connected to a spring of negligible mass having spring constant $100 \,N \,m^{-1}$ as shown in the figure. The block is released from rest with the spring in the unstretched position. The block moves $10 \,cm$ down the incline before coming to rest. The coefficient of friction between the block and the incline is (Take $g=10 \,m \,s^{-2}$ and assume that the pulley is frictionless).

Two wedges each of mass $600 \ g$ are placed next to each other on a rough horizontal surface. The coefficient of static friction between the wedges and the surface is $0.4$. $A$ cube of mass $M$ is balanced on the wedges as shown in the figure. If there is no friction between the cube and wedges,the largest mass $M$ of the cube that can be balanced without motion of the wedges is . . . . . . $kg$.

An electric lift with a maximum load of $2000\,kg$ (lift + passengers) is moving up with a constant speed of $1.5\,m/s$. The frictional force opposing the motion is $3000\,N$. The minimum power delivered by the motor to the lift in watts is: $(g=10\,m/s^2)$

$A$ cylinder is placed on a rough plank,which in turn is placed on a smooth surface. The plank is pulled with a constant force $F$. Indicate the correct direction of the friction force acting on the cylinder.