A glowing electric light bulb placed 15 cm from a concave spherical mirror produces a real image 8.9 from the mirror. the light bulb is moved to a position 20cm from the mirror
a) what is the image position? (answer with -1000 if the image does not exist)

The image will form at distance d = 7.75 cm from the mirror

Explanation:

As we know that the bulb is placed at 15 cm distance from the concave mirror

Then the image will form at distance d = 8.9 cm

now we have

so we have

Now when bulb is placed at distance 20 cm from the mirror

then again we have

now we have

t2 equal the displacement of the particle over the same time period if t2> t/2? hint: consider a sine wave starting at t1=0, then consider a closing wave starting at t1=0, for your explanatio