Question

An elevator descends into a mine shaft at the rate of 7m per minute .If it descent starts from 20 m above the ground level ,find the time taken by the elevator to reach -400m.

Answer 1

starting value : $20$
rate : $-7$

setup an equation and solve $t$
$20-7t=-400\implies\,t=60$ minutes

Answer 2

The elevator starts from 20 m above the ground.
Therefore , total distance to be covered=(400+20)m=420 m.
Speed=7 m/min.
Therefore, time=D/S
=420/7 min
=60 min
=1 hr
Ans>The time taken is 1 hour.