Page 52 - SP015 Past Years PSPM Chapter 6 -14 Ver 2020

PHYSICS PSPM SEM 1 1999 - 2017

PSPM JUN 2000/2002 SF035/2 No. 10(c)(ii)

48. f

660

550

x
Observer’s position

FIGURE 10.7

A patrol car emitting siren of frequency 600 Hz is approaching, passing, and moving
away from an observer at rest. The changes of frequency heard by the observer are
shown in FIGURE 10.7. What is the frequency heard by the observer when the patrol
car passes him? Determine the speed of the patrol car.
-1
(Speed of sound in air = 330 m s ) [8 m]

PSPM 2003/2004 SF017/2 No. 5(b)

49.

S 1 S 2

P
FIGURE 10.8

FIGURE 10.8 shows two identical sources S 1 and S 2 which are moving towards an
observer P. The two sound sources S 1 and S 2 produce notes of frequency 500 Hz. If the
-1
-1
speed of S 1 and S 2 are 20 m s and 23 m s respectively, calculate the beat frequency
-1
heard by P. (Speed of sound = 340 m s ) [4 m]

PSPM 2004/2005 SF017/2 No. 12(d)

50. The siren of a police car emits sound at frequency f. If the car is moving with speed v s
toward a stationary observer, the frequency heard by the observer is given by
f
f '
  1 v s  
 v 

where v is the speed of sound in air. Show that the frequency of the sound heard by the
observer increases.
[1 m]

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