Why do we place handles at maximum possible distance from the hinges in a door?

Why do we feel cooler under the fan?

Why do we use ball-bearings?

A convex lens of focal length 15 cm is placed in front of a convex mirror co-axially 5 cm from the mirror. The image of an object placed at a distance 20 cm from the lens found to have been formed over the object. Estimate the radius of curvature of the mirror.

A concave mirror of focal length 8cm produces a real image of size 4cm when an object 2cm high is placed at a certain distance from the mirror . Find the position of the image and the object.

Why do we need Quantum theory?

A courier-person cycles from a town to a neighbouring suburban area to deliver a parcel to a merchant. His distance from the town at different times is shown by the following graph How far is the place of the merchant from the town?

Lenses of power 3D and - 5D are combined to from a compound lens. An object is placed at a distance of 50 cm from this lens. Find the position of its image ?