A. A wire of diameter 2.8mm supports a weight W. If the tensile stress in the wire is 2 x 10⁷Nmˉ². Find the value of W )

The weight supported by the wire is 123.15 N

Explanation:

Given;

tensile stress in the wire, τ = 2 x 10⁷ Nm⁻²

diameter of the wire, d = 2.8 mm

radius of the wire, r = 1.4 mm = 1.4 x 10⁻³ m

The area of the wire is calculated as;

The weight supported by the wire is calculated as;

W = F = τ x A

W = (2 x 10⁷ Nm⁻²) X (6.158 x 10⁻⁶ m²)

W = 123.15 N

Therefore, the weight supported by the wire is 123.15 N

weight of the box is given as

here this is placed on the inclined of angle 42 degree

now this weight will have two components one is along the incline other is perpendicular to it

so here we need to apply a force parallel to incline opposite to its component of weight

so here the component of weight is given as

here we have

so it requires 75 n force to move it upwards

the answer is the first electromagnet (a). this is because it has more coils around the ferromagnetic material. increasing the number of coils increases the surface area in which the metal interacts with the current in the coil. this enables more atoms in the metal to become aligned hence becoming more magnetized.