Q$\mathrm{.}4($a$)$ Differentiate between two stroke and four stroke engine.

Q$\mathrm{.}4($b$)$ A furnace wall comprises three layers: $13\mathrm{.}5$ cm thick inside layer of fire brick, $7\mathrm{.}5$ cm thick middle layer of insulating brick and $11\mathrm{.}5$ cm thick outside layer of red brick. The furnace operates at $\backslash (870^\{\backslash$circ$\}\backslash$mathrm$\{$C$\}\backslash )$ and it is anticipated that the outside of this composite wall can be maintained at $\backslash (40^\{\backslash$circ$\}\backslash$mathrm$\{$C$\}\backslash )$ by the circulation of air. Assuming close bonding of layers at their interfaces, find the rate of heat loss from the furnace and the wall interface temperature. The wall measures $\backslash (5\backslash$mathrm$\{$~m$\}\backslash$times $2\backslash$mathrm$\{$~m$\}\backslash )$ and the data on thermal conductivities is : Fire brick $\backslash (\backslash$mathrm$\{$k$\}\_\{1\}=1\mathrm{.}2\backslash$mathrm$\{$~W$\}/\backslash$mathrm$\{$m$\}\backslash )-$deg, Insulating brick $\backslash (\backslash$mathrm$\{$k$\}\_\{2\}=0\mathrm{.}14\backslash$mathrm$\{$~W$\}/\backslash$mathrm$\{$m$\}-\backslash$mathrm$\{$deg$\}\backslash ),$ and red brick $\backslash (\backslash$mathrm$\{$k$\}\_\{3\}=0\mathrm{.}85\backslash$mathrm$\{$~W$\}/\backslash$mathrm$\{$m$\}\backslash )-$deg.

Q$\mathrm{.}5($a$)$ Explain advantages and disadvantages of renewable and nonrenewable energy resources.

Q$\mathrm{.}5($b$)$ Explain when and where tides occur? How tidal energy is harnessed for useful power utilization. Explain your answer with suitable diagrams.