Question

A convex lens has focal length of 20cm. If the image of an object is formed at 40 cm on the other side of the lens, what is the distance of the object from the lens?

Answer 1

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If you think of it this way. Suppose the mirror was not present, the lens is operating in a symmetrical mode. If the source is at 40cm from an f=20cm lens, then the image arises at 40 cm on the other side of the lens. This image now becomes a new source if we are going to reflect the object back to its original position. If we now add a mirror, it has to be set up so that ITS source and image coincide at the same location as the image of the lens, i.e. at 40cm from the lens. For a convex mirror to do this we have to write the mirror equation as

1−7.5=1−15+1−151−7.5=1−15+1−15

the minuses arising because the source and image are on the right hand side of the lens and the negative arising on the focal length of the mirror because it is convex. Hence the mirror is 40–15cm=25cm from the lens.

Answer 2

Explanation:

Answer:AT top

0  =  u – at

0 = u -10*2

u = 20 m/s (t = 2s)

u becomes final velocity for the ground projection thus,

400 = u^2 – 2*-10*25

u = 30 m/s

This would be gthe velocity.

Explanation: