Rhombus is a quadrilateral with all sides equal in length. The given information about the rhombus is the perimeter and the measure of one of its angles. We need to find the area of the rhombus.

Let's break down the problem step by step:

1. Find the length of one side:
- The perimeter of the rhombus is given as 40 cm.
- The perimeter of a rhombus is the sum of all four sides.
- Since all sides of a rhombus are equal, each side is 40 cm / 4 = 10 cm.

2. Find the length of the diagonals:
- In a rhombus, the diagonals are perpendicular bisectors of each other, and they divide the rhombus into four congruent right-angled triangles.
- The angle measure given is 60 degrees, which means each right-angled triangle has a 30-60-90 degree configuration.
- In a 30-60-90 triangle, the side opposite the 30-degree angle is half the length of the hypotenuse.
- Therefore, the length of each diagonal is twice the length of one side, which is 2 * 10 cm = 20 cm.

3. Calculate the area of the rhombus:
- The diagonals of a rhombus are perpendicular bisectors, so they divide the rhombus into four congruent right-angled triangles.
- The area of a right-angled triangle can be calculated using the formula: Area = (1/2) * base * height.
- In this case, the base is half the length of one side, which is 10 cm / 2 = 5 cm.
- The height is the length of the other side, which is 20 cm.
- Therefore, the area of each right-angled triangle is (1/2) * 5 cm * 20 cm = 50 cm^2.
- Since there are four congruent right-angled triangles in the rhombus, the total area of the rhombus is 4 * 50 cm^2 = 200 cm^2.

Therefore, the correct answer is option B) 50√3 cm^2.