## A Problem from power

Gayathri Shinde Asks:

“Please answer this question with explanation:

The power output of a machine that lifts a 600 kg

weight through a height of 20m in 1min is:

@)1.96kW b)0.98kWc)12kW d)3.92kW”

Answer:

Use the formula power = work /time

## Fundamental Quantities

Gayatri Shinde asks:

“What are the 7 fundamental quantities”

Answer:

Fundamental Physical quantities are those which can be used to express (almost) all other physical quantities but the fundamental quantities cannot be expressed in terms of each other.

There are 7 Fundamentals quantities identified

- length (unit metre (m))
- mass (unit kilogram (kg))
- time (unit second (s))
- thermodynamic temperature (unit kelvin (K))
- intensity of current (unit ampere (A))
- luminous intensity (Unit candela (Cd)) and
- amount of substance (unit mole (mol))

## Change in Resistance due to stretching a wire

Sreshtha asked:

“A piece of wire is redrawn without any change in volume so that its radius become half the original. Compare the new resistance with the original value.”

Answer:

When we redraw the wire, the volume remains constant and the resistivity also remains constant. SO, the variables are

- area of cross section and
- the length

When radius becomes half, the area of cross section increases in such a way that A1l1 = A2l2. This implies that when length is halved, area of cross section is doubled.

We know that

Therefore, the new resistance becomes (1/4) th the original value.

So, R2:R1 = 1:4