Question Discussion & Solution

The correct answer is Boy pushing wall in a room.

Key Points

• Boy pushing the wall in the room is not an example of work done.
  • When a boy pushes a wall, he is applying force on the wall. We see that the wall shows no displacement.
  • Work is given as the product of the forces and the displacement in the same direction.
  • Hence the work done is zero.

Additional Information

• Work is done when a force moves. Everyday examples of work include walking up a flight of stairs, lifting heavy objects, pulling a sled and pushing a shopping trolley, Applying pressure on a pebble lying on the surface, raising a book to a height.
  • Work is not done when holding a bag stationary or a book at arm's length because although a force is being applied, the force does not move.

The pattern is:

31

31 × 2 + 1 = 63;

63 × 2 - 2 = 124;

124 × 2 + 3 = 251;

251 × 2 - 4 = 498

Hence, the answer is '498'.

The first two statements give information about payal, monika and Sonam. Information about kunal and monika cannot be determined.

People – A, B, C, D, E and F

All are facing north.

1. C is sitting 2^nd to the left of D.

2. Only two person sits between A and B.

3. E is sitting at the extreme left end and neither F nor A is the immediate neighbour of E.

4. B is sitting to the left of A.

As, F and A are not the immediate neighbours of E, Case I is eliminated and the arrangement with the combination of Case II, thus formed is:

Hence, D is at the extreme right end.

The correct answer is Lead and Tin.

Key Points

• Soldering is the process of joining two metal objects together by a third soft metal alloy which is called solder.
• Solder is a metal alloy that melts at a lower temperature than the metals being soldered.
• A commonly used alloy is solder, which is an alloy of tin (Sn) and lead (Pb).
• The alloy of tin-lead solder is a mixture of 63% tin and 37% lead. 63/37 solder melts at 183°C.
• So, Alloy of tin (Sn) and lead (Pb) is used for welding electrical wire together.

Additional Information

• Element Tin (Sn) belongs to Group 14 of the periodic table.
  • Atomic Number - 50
  • Atomic Mass  - 118.710 amu.
• Element Lead (Pb) belongs to Group 14.
  • Atomic Number - 82
  • Atomic Mass - 207.2 amu.