Solve question number 4 plss..

First we need to find acceleration

$$\begin{gathered} v = u +at \\ 10 = 0+a\times 2 \\ a = 5 m/s^2 \\ Now weight of body -1000 N \\ mg = 1000 N \\ So \\ m = 100 kg \\ F =ma =100\times 5 = 500 N \end{gathered}$$

c)
Linear momentum of an body is defined as the product of mass and velocity. 
From second law of motion it can be state that the net external force equals the rate of change in momentum of a system with time.

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