Answer please

a$)$ Make a list of welding processes that are suitable for producing $($i$)$ butt joints, where the weld is in the form of a line or line segment, $($ii$)$ spot welds.

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b$)$ Explain why preheating the components to be welded is effective in reducing the likelihood of developing cracks.

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c$)$ A heat source transfers $250Bt\frac{u}{m}in$ to a metal surface for welding. The heated area is approximately circular, and the heat intensity decreases with increasing radius as follows: $40\%$ of the power is transferred within a circle of diameter $=0\mathrm{.}25$ in$,$ and $60\%$ is transferred within a concentric circle of diameter $=0\mathrm{.}50in.$ What are the power densities in $($i$)$ the $0\mathrm{.}25-$in diameter inner circle and $($ii$)$ the $0\mathrm{.}50-$in diameter ring that lies around the inner circle?