Question

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.

• A. 20 sec
• B. 40 sec
• C. 60 sec
• D. 80 sec

Answer 1

The correct option is B

40 sec

Distance travelled by the machine while drilling the hole= 20 cm

Speed of the machine = 0.3 m/min

1m = 100 cm

1 min = 60 seconds

Speed=0.3 m/min = $\frac{0.3\times 100}{1\times 60}=\frac{30}{60}=\frac{30/30}{60/30}=\frac{1}{2}$ cm/s = 0.5 cm/s

Speed = $\frac{Distance}{Time}$

Time = $\frac{Distance}{Speed}$ = $\frac{20}{0.5}$ = $\frac{20\times 10}{0.5\times 10}=\frac{200}{5}=40$ seconds