The voltage - length characteristic of a direct current arc in an arc welding process is $$V=$$ $$(100+40l),$$ where $$l$$ is the length of the arc in $$mm$$ and $$V$$ is arc voltage in volts. During a welding operation, the arc length varies between $$1$$ and $$2$$ $$mm$$ and the welding current is the range $$200$$-$$250A$$. Assuming a linear power source, the short circuit current is _____________$$A.$$

For a certain job, the cost of metal cutting is $$Rs.18C/V$$ and the cost of tooling is Rs.$$270C/(TV).$$ Where $$C$$ is a constant, $$V$$ is the cutting speed in $$m/min$$ and $$T$$ is the tool life in minutes. The Taylor's tool life equation is $$V{T^{0.25}} = 150.$$ The cutting speed (in $$m/min$$) for the minimum total cost is ___________

The following data is applicable for a turning operation. The length of job is $$900$$ $$mm,$$ diameter of job is $$200$$ $$mm,$$ feed rate is $$0.25$$ $$mm/rev$$ and optimum cutting speed is $$300$$ $$m/min.$$ The machining time (in $$min$$) is _____________

For the situation shown in the figure below the expression for $$H$$ in terms of $$r, R$$ and $$D$$ is