Answer :
Final answer:
The elevator travels a total distance of 490 meters (from 10 m above the ground to -480 m). At a descent rate of 7 meters per minute, it will take exactly 70 minutes to reach -480 meters.
Explanation:
To determine how long it will take for the elevator to reach -480 m from 10 m above ground level, we need to find the total distance the elevator must travel and then divide this distance by the rate of descent. The elevator starts 10 m above the ground and must travel to -480 m, which is a total distance of:
480 m (from ground to the target depth) + 10 m (from the starting point above ground to ground level) = 490 m.
Since the elevator descends at a rate of 7 m per minute, we can calculate the time taken to travel 490 m by dividing the total distance by the rate of descent:
490 m ÷ 7 m/minute = 70 minutes.
Therefore, the correct answer is (a) 70 minutes.
