Laws of Motion

A lead block is suspended from your hand by a string. The reaction due to the force of gravity on the block is the force exerted by :
An object of mass $$2\ kg$$ is placed in a frame $$(s_{1})$$ moving with velocity $$10\vec {i} + 5\vec {j} m/s$$ and having acceleration $$5\vec {i} + 10\vec {j} m/s^{2}$$. This object is also seen by an observer standing in frame $$(s_{2})$$ moving with velocity $$5\vec {i} + 10\vec {j} m/s$$. The net force acting on object with respect to $$s_{2}$$ frame is
During a planned manoeuvre in a space flight, a free-floating astronaut A pushes another free-floating astronaut B, the mass of A being greater than that of B. Then, the magnitude of the force exerted by astronaut A on astronaut B is 
In the above problem, during a push 
Three masses m, m and 2 m are held stationary as shown in the figure with all the strings taut. Now, the mass 2 m is released and it starts falling vertically downward.

Velocity of masses m at the instant 2m touches the gound is
What is net Force?