Motion in a Plane - Result Question 47

50. A stone tied to the end of a string of $1 m$ long is whirled in a horizontal circle with a constant speed. If the stone makes 22 revolutions in 44 seconds, what is the magnitude and direction of acceleration of the stone?

[2005]

(a) $\pi^{2} m s^{-2}$ and direction along the radius towards the centre

(b) $\pi^{2} m s^{-2}$ and direction along the radius away from the centre

(c) $\pi^{2} m s^{-2}$ and direction along the tangent to the circle

(d) $\pi^{2} / 4 m s^{-2}$ and direction along the radius towards the centre

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Answer:

Correct Answer: 50. (a)

Solution:

(a) $a_r=\omega^{2} R & a_t=\frac{d v}{d t}=0$

or, $a_r=(2 \pi n)^{2} R=4 \pi^{2} n^{2} R^{2}=4 \pi^{2}(\frac{22}{44})^{2}(1)^{2}$

$a _{\text{net }}=a_r=\pi^{2} ms^{-2}$ and direction along the radius towards the centre.

2 If the force acting on a particle is always perpendicular to the velocity of the particle, then the path of the particle is a circle. The centripetal force $(F_c)$ is always perpendicular to the velocity of the particle, i.e., $F_c \perp v$