The Special Theory of Relativity

On passing through a wooden sheet a bullet loses $$1/20$$ of initial velocity. The minimum number of sheets required to completely stop the bullet will be:
Who proposed general theory of relativity?
What is the famous relation in physics which  relates 'moving mass' m to the ' rest mass ' $$m_{0}$$ of particle in terms of its speed v and the speed of light c. (this relation first arose as a consequence of special relativity)
What is the reason for constant speed of light for all the observers ? 
A block of mass $$4kg$$ and dimensions $$10cm\times 20cm\times 30cm$$ rests on the floor. If $$g=10m$$ $$s^{-1}$$, then the maximum pressure the block can exert on the floor is