Example 5 Suppose we represent the distance above the ground by a positive integer and that below the ground by a negative integer, then answer the following: (i) An elevator descends into a mine shaft at the rate of 5 metre per minute. What will be its position after one hour?
Elevator goes down at rate of 5 metre per minute
Therefore,
Position of elevator after 1 minute = −5m
Position of elevator after 60 minute = −5 × 60 m
= −300 m
Elevator is 300 m below ground level.
Example 5 Suppose we represent the distance above the ground by a positive integer and that below the ground by a negative integer, then answer the following: (ii) If it begins to descend from 15 m above the ground, what will be its position after 45 minutes?
Initially,
Elevator is 15 m above ground
∴ Initial Position = +15 m
Now,
Elevator moves down for 45 minutes
Distance elevator moves in 1 minute = −5 m
Distance elevator moves in 45 minute = −45 × 5 m
= −225m
∴ Final position of elevator = Initial position
+ Distance it moves in 45 minutes
= 15 + (−225)
= 15 − 225
= − (−15 + 225)
= − (225 − 15)
= −210 m
∴ Position after 45 minutes is −210 m
i.e. Elevator is 210 m below ground level

Made by

Davneet Singh

Davneet Singh is a graduate from Indian Institute of Technology, Kanpur. He has been teaching from the past 12 years. He provides courses for Maths and Science at Teachoo.