Question

The pieman now walks with speed 30 m/min towards the receiver while continuing to put pies on the belt at 20 per minute. Find the spacing of the frequency with which they are received by the stationary pieeater.

• A. $13.5/m,22.22mi{n}^{-1}$
• B. $15/m,22.22mi{n}^{-1}$
• C. $135/m,22.22mi{n}^{-1}$
• D. $3/m,22.22mi{n}^{-1}$

Answer 1

The correct option is A $13.5/m,22.22mi{n}^{-1}$

The problem is a Doppler effect analogy.

$f=20/min$

$v=300m/min$

$v_s=30m/min$

$\therefore f^{\prime }=f\left(\frac{v}{v-v_s}\right)=20\left(\frac{300}{300-30}\right)=22.22mi{n}^{-1}$