Question

A stone tied at the end of a string 80 cm long is whirled in a horizontal circle with a constant speed. If the stone makes 25 revolutions in 14 s, what is the magnitude of acceleration of the stone?

• A. $90 \,m / s ^{2}$
• B. $100 \,m / s ^{2}$
• C. $110 \,m / s ^{2}$
• D. $120 \,m / s ^{2}$

Answer 1

Answer: (B)

Length of the string, $l=80 \,cm =0.8 \,m$
Number of revolutions $=25,$ Time taken $=14 \,s$
$\therefore v =\frac{25}{14}=1.78 \,s ^{-1}$
$\therefore \omega=2 \pi v=2 \pi \times 1.78=11.18 rad / s $
$ a=\omega^{2} l=(11.18)^{2} \times(0.8)$
$=99.99 \,m / s ^{2} \approx 100\, m / s ^{2}$