Question

The number of revolutions of a current meter in 50 seconds were found to be 12 and 30 corresponding to the velocities of 0.25 and 0.46 m/s respectively. What velocity (in m/s) would be indicated by 50 revolutions of that current meter in one minute?

• A. 0.42
• B. 0.50
• C. 0.60
• D. 0.73

Answer 1

The correct option is C 0.60

Equation of current meter
$V=a{N}_s+b\dots \dots \left(i\right)$

Here,
$V=$ Stream velocity at the instrument location in m/s
$N_s=$ Revolution per second of the current meter
$a,b=$ Constants of current meter

From (i)
$0.25=a\times \frac{12}{50}+b\dots \dots \left(ii\right)$

$0.46=a\times \frac{30}{50}+b\dots \dots \left(iii\right)$

From (ii) & (iii)
$a=0.583,b=0.11$

From (i)
$V=0.583N_s+0.11$

$=0.583\times \frac{50}{60}+0.11$

$=0.6\text{m/s}$