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## Homework Statement

You are in your car driving on a highway at 25 m/s when you glance in the passenger-side mirror (a convex mirror with radius of curvature 150 cm) and notice a truck approaching. If the image of the truck is approaching the vertex of the mirror at a speed of when the truck is 2.0 m from the mirror, what is the speed of the truck relative to the highway?

## Homework Equations

## The Attempt at a Solution

(sorry my bad english)

Assuming both the truck and the car speeds to be constant, the truck takes the same time interval as its image to reach the vertex of the mirror. So,

1 / f = 1 / s + 1 / s'

-1 / 0.75 m = 1 / 2 m + 1 / s'

s' = -0.54 m

t = -0.54 m / -1.9 m /s

[ (V - 25) m / s ] t = 2 m

but solving this for V I didnt find the correct value: 51 m / s. Maybe the speed is'nt constant?

My sketch: