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# When a ceiling fan is switched on, it makes 10 rotations in the first 3 seconds. Assuming uniform angular acceleration, of how many revolutions it will make in the next 3 seconds?

$\begin {array} {1 1} (a)\;10 & \quad (b)\;20 \\ (c)\;30 & \quad (d)\;40 \end {array}$

Can you answer this question?

$\theta= \large\frac{1}{2} \alpha t^2$
$2 \pi \times 10 =\large\frac{1}{2}$$\alpha (3)^2 2 \pi n= \large\frac{1}{2}$$ \alpha (6)^2$
$n$- total number of rotation in 6 seconds
$\large\frac{n}{10}=\frac{36}{9}$
$n=40$
the number of rotations in the first 3 second is 10. therefore the number of rotations in the next 3 seconds is
$\therefore \;n_1+n_2=n=40$
$n_2= 40-10=30$

answered Nov 25, 2013 by
edited Jul 28, 2014