A carpenter needs to drill a hole in the wooden plank using a drilling machine. The depth of the hole to be drilled is 20cm. Find the time required to drill the hole if the machine drills at a speed of 0.3 m/min.

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Find the speed range ratio for the drilling machine spindle if the minimum and maximum diameters of drills used are 5mm and 25mm respectively and if the machinability indices for the work materials are 120 (brass) and 40 (alloy steel)

The correct option is D 15Speed range ratio, =VmaxVmin×DmaxDmin=12040×255=3×5=15

Find the speed range ratio for the drilling machine spindle if the minimum and maximum diameters of drills used are $5 m m$ and $25 m m$ respectively and if the machinability indices for the work materials are $120$ (brass) and $40$ (alloy steel)

The correct option is D $15$
Speed range ratio,
$= \frac{V_{m a x}}{V_{m i n}} \times \frac{D_{m a x}}{D_{m i n}} = \frac{120}{40} \times \frac{25}{5} = 3 \times 5 = 15$