Chapter 6, Problem 91RE

To determine

To Calculate: Rotation speed of beam of lighthouse.

Answer to Problem 91RE

The required rotation speed is $0.63rad/s$ .

Explanation of Solution

Given information:

lighthouse has dual beam (opposite to each other).

Ship observes blinking light after 5 second.

Formula used:

Angular velocity or rotation speed of any object doing circular motion is given by

  $Rotationspeed=\frac{\theta }{t}$

As lighthouse has dual beam (opposite to each other), So the lighthouse will rotate ${180}^{°}$ between two blink of beam on a ship.

  $Rotationspeed=\frac{\theta }{t}$

As we know, ${180}^{°}=\pi$

A Ship observe blink after 5 second.

  $\begin{array}{l}Rotationspeed=\frac{\pi }{5}\\ =\frac{22}{7\times 5}\\ =0.63rad/s\end{array}$

The required rotation speed is $0.63rad/s$ .