Question

When a ceiling fan is switched on, it makes 10 revolution in the first 3 s. Assuming a uniform angular acceleration, how many rotation it will make in the next 3 s?

• A. 10
• B. 20
• C. 30
• D. 40

Answer 1

The correct option is C 30

Let the angular acceleration be $\alpha$.

From the given data:

$\Rightarrow 10\times 2\pi =\frac{1}{2}\alpha (3{)}^2$

$\Rightarrow 20\pi =\frac{9\alpha }{2}$

Let us take revolution for first six seconds:

$\Rightarrow {\theta }_o=\frac{1}{2}\alpha (6{)}^2=18\alpha =80\pi$

The no. of revolutions in first six seconds are 40.

The no. of revolutions in the last three seconds $=40-10=30$ revolutions