
suppose you have that block hanging from the ceiling by a rope. As you can see, two forces act on the block, the tension force T and the weight W. let's assume that the tension is 10 Newton. So, using the second law of newton:

the system is static, there is no acceleration, therefore:

the weight is equal to the product of the mass and the gravitational constant:
![\begin{gathered} W=mg \\ \text{where:} \\ g\approx9.8 \\ so\colon \\ 9.8m-10=0 \\ \text{solve for m:} \\ m=(10)/(9.8) \\ m=1.02\operatorname{kg} \end{gathered}]()