Consider an elliptically shaped rail PQ in the vertical plane with $\mathrm{O}\mathrm{P}\mathrm{ }=\mathrm{ }3\mathrm{ }\mathrm{m}$ and $\mathrm{O}\mathrm{Q}\mathrm{ }=\mathrm{ }4\mathrm{ }\mathrm{m}$ . A block of mass 1 kg is pulled along the rail from P to Q with a force of 18 N, which is always parallel to line PQ (see the figure given). Assuming no frictional losses, the kinetic energy of the block when it reaches Q is $(\mathrm{n}\times 10)$ Joules. The value of n is (take acceleration due to gravity = $10\mathrm{ }\mathrm{m}{\mathrm{s}}^{–2}$ )

Hence, the correct answer is 5.