Question

A motor cycle starts from rest and accelerates along a straight path at $2$ $m/s^2$. At the starting point of the motor cycle, there is a stationary electric siren. How far has the motor cycle gone when the driver hears the frequency of the siren at $94\%$ of its value when the motor cycle was at rest?

(Speed of sound $=330m/s$)

• A. $49$ $m$
• B. $98$ $m$
• C. $147$ $m$
• D. $196$ $m$

Answer 1

Answer: (B)

$98$ $m$

$V=\sqrt{2aS}=\sqrt{4S}$
Also, $94=100(\frac{330-V}{330})=\frac{33\times 6}{10}=\sqrt{4S}$
$\Rightarrow S=98m$