A hot‑air balloon starts 40 m above ground level. It descends at a constant rate of 5 m/s. How many seconds will it take for the balloon to reach a depth of 30 m below ground level?

Step-by-step solution

1. Identify the initial height: $+40$ m (above ground).
2. Identify the final depth: $-30$ m (below ground).
3. Compute the total vertical change required: $-30-(+40)=-70$ m.
4. Since the balloon moves downward, the rate of descent is 5 m/s.
5. Use time = distance ÷ speed: $70\text{ m}÷5\text{ m/s}=14$ s.
6. The balloon will reach the desired depth after 14 seconds.

Concept tested: Negative distances and rates

Published 7 October 2026 · How this solution was prepared and checked