There is a concave mirror of focal length 7.5 cm. Two objects P and Q are placed in front of this concave mirror one by one. Heights of the images of P and Q are found to be same. Height of P is double to that of height of Q and is placed at a distance 15 cm from the mirror. At what distance object Q was placed?

Explanation

To solve the problem, we will use the mirror formula and the magnification formula for concave mirrors.

### Step-by-Step Solution:

1. **Identify Given Data**:
- Focal length (f) of the concave mirror = -7.5 cm (negative because it's a concave mirror).
- Height of object P (h_P) = 2 * height of object Q (h_Q).
- Distance of object P from the mirror (u_P) = -15 cm (negative as per sign convention).
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