The correct option is A 45 m/s
For the given concave mirror,
u=−20 cm, f=−15 cm
Using mirror formula,
1v−120=−115
⇒1v=−160
⇒v=−60 cm
So, m=−vu=−(−60)−20=−3
Also, velocity of the image when the object is moving along the principal axis,
vi,m=−m2vo,m
⇒vi,m=−(−3)2×5=−45 m/s
Hence, the speed of the image will be 45 m/s.
Why this question?Caution: While applying formula of magnification and image velocity, alwaystake care of sign convention.