The shadow cast by a simple stick or obelisk allowed ancient people to:

• A. Calculate the speed of sound
• B. Measure the passage of time during the day
• C. Find the boiling point of water
• D. Determine the mass of objects

Answer: (B)

Verified step by step guidance

1. Understand the context: The problem is about the use of shadows cast by a stick or obelisk in ancient times.
2. Recall that shadows change length and position as the sun moves across the sky, which is related to the passage of time during the day.
3. Recognize that by observing the shadow's length and direction, ancient people could track the time of day, effectively measuring the passage of time.
4. Note that this method does not relate to calculating the speed of sound, finding the boiling point of water, or determining mass, as those require different tools and principles.
5. Conclude that the primary use of the shadow cast by a stick or obelisk was to measure the passage of time during the day.