Question

human hair grows with an average speed of 3.5×10⁻⁹ m/s. how long does it take hair to grow 0.30 m? note: 1 yr = 3.156×10⁷ s.
2.7 yr
1.3 yr
1.9 yr
0.37 yr
5.4 yr

Explanation:

Step1: Use speed - time - distance formula

We know that speed $v=\frac{d}{t}$, so $t = \frac{d}{v}$. Given $d = 0.30\ m$ and $v=3.5\times 10^{-9}\ m/s$. Then $t=\frac{0.30}{3.5\times 10^{-9}}\ s$.

Step2: Calculate the time in seconds

$t=\frac{0.30}{3.5\times 10^{-9}}\ s=\frac{0.30}{3.5}\times10^{9}\ s\approx0.0857\times 10^{9}\ s = 8.57\times 10^{7}\ s$.

Step3: Convert seconds to years

Since $1\ yr = 3.156\times 10^{7}\ s$, then the time in years $T=\frac{8.57\times 10^{7}}{3.156\times 10^{7}}\ yr$.
$T=\frac{8.57}{3.156}\ yr\approx 2.7\ yr$.

Answer:

A. 2.7 yr