SPEED UNITS — Identify the correct application. Question: The knot is a unit of speed typically used for which of the following?

Introduction / Context:
A “knot” is the standard speed unit in maritime navigation, defined as one nautical mile per hour. It is also widely used in aviation, but historically it comes from seafaring practice. This item checks recognition of the primary traditional domain.

Given Data / Assumptions:

• 1 knot = 1 nmi/h, where 1 nmi = 1852 m.
• Ships and aircraft commonly report speeds in knots for navigational consistency.
• Waves (light or sound) use different speed descriptors and contexts.

Concept / Approach:
Because the nautical mile and knots form a pair, and because charts and routes were first standardized at sea, “ship” is the best-fit answer among the choices given. Although aeroplanes also use knots, the question typically expects the maritime association.

Step-by-Step Solution:
Recognize definition: knot = nmi per hour.Link to nautical domain: ships navigate using nautical miles.Select “ship.”Note that aviation also uses knots, but the origin is maritime.

Verification / Alternative check:
Bridge logs and maritime Automatic Identification System (AIS) display ship speeds in knots; flight instruments likewise show knots, but the traditional association remains nautical.

Why Other Options Are Wrong:
A) Aeroplanes do use knots, but the canonical association is maritime; the option set expects “ship.”B) Light waves have speed c in m/s, not knots.D) Sound waves are discussed in m/s or km/h.E) Trains use km/h or mph.

Common Pitfalls:
Overlooking that multiple domains use knots. In exam settings, choose the maritime answer unless the question specifies aviation.

Final Answer:
ship