What will be the velocity of a 0.23 kg arrow having a potential energy of 61 J after it is shot from a bow?

How does the image distance (di) of a convex lens compare with the image distance of a concave lens? a. the image distance of the convex lens is positive, and that of the concave lens is negative. b. both are negative for a virtual image. c. both are positive for a virtual image d. the image distance of the convex lens is negative, and that of the concave lens is positive.

What is the mass of the same rock on the earth

Idon’t quite understand this problem