How Far Should you Sit From Your Screen!

How far should an object be from a concave spherical mirror of radius 36 cm to form a real image one-ninth its size?

By the term velocity of rain, we mean velocity with which raindrops fall relative to the ground. In absence of wind, raindrops fall vertically and in presence of wind raindrops fall obliqucly. Moreover raindrops acquire a constant terminal velocity due air resistance very quickly as they fall toward the carth. A moving man relative to himself observes an altered velocity of raindrops. Which is known as velocity of rain relative to the man. It is given by the following equation. vec(v)_(rm)=vec(v)_(r)-vec(v)_(m) A standstill man relative to himself observes rain falling with velocity, which is equal to velocity of the raindrops relative to the ground. To protect himself a man should his umbrella against velocity of raindrops relative to himself as shown in the following figure. Rain is falling vertically with velocity 80 cm/s. (a) How should you hold your umbrella ? (b) You start walking towards the east with velocity 60 cm/s. How should you hold umbrella ? (c) You are walking towards the west with velocity 60 cm/s. How should you hold your umbrella ? (d) You are walking towards the north with velocity 60 cm/s. How should you hold your umbrella? (e) You are walking towards the south with velocity 80 cm/s. How should you hold your umbrella ?