The gravitational force acting between two objects is dependent on the mass of the objects and the distance by which they are separated.
For two objects with mass `m_1` and `m_2` and separated by a distance r, the gravitational force of attraction is equal to `F = (G*m_1*m_2)/r^2` where G is a constant equal to 6.67384*10^-11 m^3/(kg*s^2). On the Earth, the gravitational force of attraction on an object due to the Earth is equal to m*9.8 where m is the mass of the object.
In the problem, a string with radius 1.25 m holds a mass at one end and it is being rotated in the horizontal plane. This does not alter the gravitational force of attraction acting on the mass.
For an object with mass 50 g, the gravitational force of attraction is 50*10^-3*9.8 = 0.490 N and the gravitational force of attraction for the object with mass 70 g is 0.686 N