Question

A $20\text{H.P.}$ motor is used in a lift of a building which has $15$ floors. The height of the building is $60\text{m}$ and assuming that all the floors are of the same height, find the time taken by the motor in lifting the empty $1500\text{kg}$ lift from the ground floor to ${10}^{\text{th}}$ floor.

Answer 1

Given, the H.P. of the motor is $20\text{H.P.}$

So, the power will be,
$\text{P}=20\times 750=15,000\text{W}(1\text{H.P.}\approx 750\text{W})$
The floors are of equal height and the entire building is $60\text{m}$ tall with $15$ floors.
Hence, each floor will be $4\text{m}$.
The height to the ${10}^{\text{th}}$ floor will be $40\text{m}$.

Given the mass of the lift is $1500\text{kg}$. So,
$\text{W}=1500\times 10\times 40=6,00,000\text{J}$
We know,
$\text{P}=\frac{\text{W}}{\text{t}}$
$⟹15,000=\frac{6,00,000}{\text{t}}$
$⟹\text{t}=\frac{6,00,000}{15,000}=40\text{s}$