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An object 'O' is placed at a distance of 100 cm in front of a concave mirror of radius of curvature 200 cm as shown in the figure. The object starts moving towards the mirror at a speed 2 cm/s. The position of the image from the mirror after 10 s will be at ______ cm.

Asked in JEE Main 28th July 2nd Shift 2022 · Mirror formula and magnification

Figure: Mirror formula and magnification
Answer: 400

Step-by-step solution

f=-100 cm. After 10 s the object has moved 20 cm, so u=-80 cm.

1/v=-1/(100)+1/(80)=1/(400)

v=+400 cm, a virtual image 400 cm behind the mirror.

→ 400

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