An object that is 47.5 cm tall forms an image that is 38.6 cm tall and 14.8 cm from a spherical mirror. How far is the object from the mirror?
A) 124 cm
B) 18.2 cm
C) 47.6 cm
D) 12.0 cm

Question

Quizplus · Accepted Answer

The magnification (m) of a mirror is given by the ratio of the image height (hi) to the object height (ho), and also by the ratio of the image distance (di) to the object distance (do), so m = hi/ho = -di/do. Plugging in the given values, 38.6 cm / 47.5 cm = -14.8 cm / do. Solving for do gives do = -14.8 cm * (47.5 cm / 38.6 cm), which calculates to approximately 18.2 cm. The negative sign indicates the direction relative to the mirror surface, but the distance itself is positive.

An Object That Is 47