Questions

$pwd - present working directory

It is ABACUS.

Words formed are as below 

BUS
CAB
CUB
US

Black Mamba

Mass means the amount of matter in an object. Anything that has Mass and takes up Space is called Matter.

The Study of Matter and and how matter changes is called Chemistry.

Matter has some mass and occupies some space. Space occupied by an object is called its Volume.

• A 360-foot-high (110 metres) flag post, said to be the country's tallest, was inaugurated at the Indo-Pak Attari Border, just a stone's throw from Pakistan.
• Punjab Minister Anil Joshi inaugurated the country's largest tricolour on the tallest flag post - measuring 110 metres in length, 24 metres in width and 55 tons in weight. Built at an approximate cost of Rs 3.50 crore, the post was a project of the Amritsar Improvement Trust Authority of the Punjab Government.

A Carpet is the pet which always stays on the floor.

A Slip ring is a ring in a dynamo or electric motor which is attached to and rotates with the shaft, passing an electric current to a circuit via a fixed brush pressing against it.

Slip rings are usually made of Phosphor Bronze.

Slip ring motors usually have a 'phase-wound' rotor. This type of rotor has a 3-phase, double-layer, distributed winding consisting of coils used in alternators. The rotor core is made up of steel laminations which have slots to accommodate formed 3-single phase windings.