Answer:
Dalton's Atomic Theory states that :-
1) All matter is made up of very tiny particles called atoms.
2) Atoms are indivisible particles , which can't be created or destroyed in a chemical reaction.
3) Atoms of a given element are identical in mass & chemical properties.
4) Atoms of very different elements have different masses & chemical properties.
5) Atoms combine in the ratio of small whole numbers to form compounds.
6) The relative number & kinds of atoms are constant in a given compound.
It's drawback's are :-
1) Atoms can be divided further into electrons , protons & neutrons.
2) According to Dalton Atomic Theory, atoms of an element are identical in mass, size and many other chemical or physical properties. But, practically we observe that atoms of several elements differ in their densities and masses. These atoms with the different masses are known as isotopes. For example, Chlorine (Cl) has 2 isotopes with the mass numbers of 35 and 37.
3) Also, according to Dalton Atomic Theory, atoms of two-different elements differ in mass, size and many other chemical or physical properties. However, this is not correct for all situations. For example, Argon (Ar) and Calcium (Ca) atoms, each have an atomic mass of 40 amu. These atoms with similar atomic masses are isobars.
4) Dalton Atomic Theory fails to explain the existence of allotropes. For example, Dalton atomic theory fails to explain the differences in properties of charcoal, graphite, and diamond (which are the allotropes of carbon).
, the gravitational force is 
and the mass of the Earth is 
, therefore we can rearrange the previous equation to find m2, the mass of the telescope: