Question

A 10 cm object is located 15 cm from the concave mirror with the focal length of 5 cm. An Image  7 cm from the mirror is detected, find its height

Answer 1

According to the magnification equation (see https://www.physicsclassroom.com/class/refln/Lesson-3/The-Mirror-Equation):

$$\dfrac{h_i}{h_o} = -\dfrac{d_i}{d_o}$$

where $h_i$ is the required height of the image, $h_o = 10cm, d_i = 7cm, d_o=15cm$. Thus, obtain:

$$h_i =\dfrac{h_od_i}{d_o} = \dfrac{10cm\cdot 7cm}{15cm} \approx4.7cm$$

Answer. 4.7cm.