It is not clear to me whether the barricade is along a perimeter of a rectangular area or square area. It is not clear the barricade is along the highway in a line. I assume that there is a single line of hollow cones along 81 meters.
Diameter of a hollow cone = 50 cm
Distance between the centers of two successive cones = 1 meter. In one meter There is one cone and 50 cm of free space.
a) Number of hollow cones used = 81 m / 1m = 81
b) Lateral Surface area of each cone : π R L
If the cone is pained inside and outside both surfaces then = 2 π R L
L² = H² + R² = 25² + 100² = 25² * 17
L = 25√17 cm
Cost = Rs 2 π * 0.25 * 0.25 * √17 * 15 = Rs 15 π √17 / 8
Because the center of gravity is higher above the ground. Their stability is less and danger of overturning is more. The vertical line passing through CM passes through the base of the truck for only smaller angles of tilt. So that line can fall outside the base, for smaller angles of tilt (or smaller torque).
Recycling reduces wastage. Recycling enables energy saving as production of fresh material amounts can be reduced. It reduces cutting of trees or less use of chemicals. It enables easier waste management also. Recycled materials may be cheaper. Pollution will be reduced.
Recycled materials : 1) plastic toys, bottles 2) glass bottles, jars, mirrors, panes & container, 3) Rubber 4) paper.