An object of $20 \mathrm{kg}$ is raised through a height of $4 \mathrm{m}$. What is the work done?  Take $\mathrm{g} = 9.8 \mathrm{m}/{\mathrm{s}}^2$.

The amount of work done on a body is obtained by calculating the dot product of the force and the displacement. 

We know that, $\mathrm{Force} = \mathrm{mg} = 20\times 9.8= 196 \mathrm{N}$

Distance = 4 m

We know that, 

 $$\begin{gathered} \mathrm{Work} \mathrm{done} = \mathrm{Force} \times \mathrm{Distance} \\ = 196\times 4 \\ = 784 \mathrm{J} \end{gathered}$$ 

Hence, the correct option  is A).