I don’t know but I hope someone helps you
Focal length is the distance between the center of a convex lens or a concave mirror and the focal point of the lens or mirror — the point where parallel rays of light meet, or converge. From the optics the focal length of the mirror can be defined as the radius of the mirror divided between two, or in other words, half the radius of the mirror.
Therefore the focal length of the mirror is 17cm
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You COULD find acceleration by taking a lot of distance measurements,
but that's definitely the hard way to do it.
Acceleration is (change in speed) divided by (time for the change).
So the basic way to calculate acceleration is to measure the change
in speed, not distance.