The Doppler effect is an effect produced by a moving source of sound or electromagnetic waves due to the relative motion of a source or a receiver. If an emergency vehicle approaches Bob and moves away from Jill, how does the frequency of the siren change?

A) Neither Bob or Jill perceive any change in the frequency of the siren.
B) As an emergency vehicle approaches Bob the frequency appears to increase.
C) As an emergency vehicle moves away from Jill the frequency appears to increase.
D) Bob does not notice any change until the vehicle passes him and the siren increases.

Answer: d. 39 cmin the diagram, the approximate length of the minor arc de is 39 centimetres.step-by-step explanation: the formula for the length of an arc in a circle is as displayed below.let the length of the minor arc de = xx = 2( pi )r × angle of sector / 360°from this, we will substitute the values given from the problem into the formula to obtain the length of the minor arc de.x = 2( pi )r × angle of sector / 360°r = radius = 25cmpi as an approximate value = 3.14angle of sector = 120°x = 2( 3.14 )( 25 ) × 120° / 360°x = 157 × 1 / 4x = 39.25x = 39 ( rounded to the nearest whole number as an approximate value )