=319Hz
Explanation:
This question is on sound waves
General formulae;
Frequency of observer= f of source*[ (v of sound+ v of observer)/(v of sound-v of source)]
where f is frequency and v is velocity
Given;
Velocity of sound = 340m/s
frequency of source = 300 Hz
Velocity of observer=0m/s
Velocity of source/truck= 20m/s
Substitute values in the formulae;
Frequency of observer= 300× {(340+0)/(340-20)}
=300×{ 340/320}
=300×340/320
=318.75
=319Hz
4.494×10^-4cm
Explanation:
height of object=142cm
obj.distance=250cm
focal length=15cm
height of image=x
v=uf/u-f
v=(250)(15)/250-15
v=15.957cm
height of image/height of object=image distance /object distance
x/142=15.857/250
250x=15.957/142
x=15.957/142×1/250
x=4.494×10^-4cm