Impression of an image stays in the retina for:

Q. The impression of an image does not vanish immediately from the retina. It persists there for about $1/{16}^{th}$ of a second.

Q. An echo of the sound produced can be heard only if it reaches our ear after -

Q. Fill in the blank :
The impression of an image lasts on the retina for ............. of a second

Q. A ball of mass $50g$ is dropped from a height of $20m$. A boy on the ground hits the ball vertically upwards with a bat with an average force of $200N$, so that it attains a vertical height of $45m$. The time for which the ball remains in contact with the bat is (Take $g=10m/s^2$)