A block of mass 20 kg slides on a rough horizontal plane surface. Let the speed of the block at a particular instant is 10 m/s. It comes to rest after travelling a distance of 20 m. Which one of the following could be the magnitude of the frictional force?

Given below are the four cases in which certain heat transfer is taking place:

1. Ice is melting in a glass full of water

2. Water is boiling in an open container

3. A metal rod is heated in a furnace

4. A cup of coffee is allowed to cool on a table

In which of the above cases, the Newton's Law of Cooling is applicable ?

The figure given below shows the direction of the two forces P and Q acting on a skydiver :

Which one among the following statements is correct about the two forces?

An infinite combination of resistors, each having resistance $R = 4 \Omega$, is given below. What is the net resistance between the points A and B? (Each resistance is of equal value, $R = 4 \Omega$)