The circular metal plate has a concentric circular hole .if the plate is heated uniformly ,so that the outer circumference of the plate increase by 4%,then the circumference of hole will be?

If you assume that the plate expands uniformly, then the circumference of a central hole will increase at a rate proportional to its radius. So if the hole is 1/2 the diameter of the plate, I would expect its circumference to increase 1/2 as much as the outer circumference of the plate.

A cube of mass 5 kg is placed on the top of another cube of mass 6 kg on a friction less table. A horizontal force of 15N must be applied to stop the top cube to cause to slip on the bottom block . Find the maximum horizontal force that must be applied to the lower block so that both the cubes will move together . Also find the resulting acceleration.

Three charges q1 q2 q3 .distance from q1 to q2 is d and from q2 to q3 is l.find the total electric field at the location of each charge...