What frequency will you hear if a truck is driving toward you at 20 m/s sounding

=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