Question

An elevator descends into a mine shaft at the rate of $15$ m/min. If the descend starts from $10$ m above the ground level, how long will it take to reach $-140$ m?​

• A. $18$ minutes​
• B. $10$ minutes​
• C. $38$ minutes​
• D. $8$ minutes​

Answer 1

The correct option is B $10$ minutes​

Initial position of the elevator $=10\text{m}$ above the ground
The elevator must reach $-140\text{m}$.
So, the elevator will have to descend $=10-(-140)=150\text{m}$ in total to reach $-140\text{m}$.

Given: Lift descends at the rate of $15$ m/minute.
To descend $15$ m $⟹$ lift takes $1$ minute
To descend $150$ m $⟹$ elevator takes $=\frac{150}{15}=10$ minutes
Therefore, the elevator will take $10$ minutes.