Question

A 4-inch by 2-inch piece of granite that is 5 feet long is cut lengthwise along its diagonal. Find the perimeter and area of the cross section formed by the cut.

Answer 1

Perimeter of the cross section = (10+4√5)inches = 18.9in

Area of the cross section= = 10√5 in²

Explanation:

Find attached the diagrams used in solving the question

Dimensions of granite = 4in by 2in

Length = 4in

Breadth = 2in

Height = 5in

When granite is cut lengthwise along it's diagonal, the cross section formed by the cut will be a rectangle.

Perimeter of the cross section = 2(height+breadth)

Breadth = diagonal of the cross section

The diagonal of a rectangle divides the rectangle into two right angled triangles.

We would apply Pythagoras theorem to find the length of the diagonal

Hypotenuse ² = opposite ²+adjacent ²

Hypotenuse = length of diagonal

Hypotenuse ² = 2² + 4²

Hypotenuse ² = 4+16 = 20

Hypotenuse = √20 = 2√5

Perimeter of the cross section = 2(height+breadth) =2(5+2√5)

Perimeter of the rectangle = 10+4√5 inches = 18.9in

Area of the cross section= diagonal × height

Area of the cross section= 2√5 × 5

Area of the cross section= = 10√5 in²