a block of mass m is placed against the vertical surface by a spring of unstretched length l if the coefficient of friction between the block and the surface is u then choose the correct statement

1. if spring constant k= 2mg/ud block will not be in equilibrium
2. minimum spring constant k min to keep block of mass m in equilibrium is mg/ud
3. if spring constant is k= 2mg/ud the normal reaction is mg/u
4. in part c force of friction is mg/u

Three identical balls are placed on a frictionless horizontal surface touching each other. They stick to each other because of adhesive. Another ball of same radius and mass m is placed over the void created by the three balls. Find the forces applied by the balls kept on the floor to each other if the system remains in equilibrium.

A car loaded with water having total mass 1000 kg moves on a straight horizontal Road starting from rest under the action of a force of 100 Newton. The water spills throw a small hole in the bottom at a rate of 0.1 KG per second the velocity of cart after 300 seconds is nearly.

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