A wave has a frequency of 50 Hz and a wavelength of 4 m. Its speed is:

## The reasoning This is the **wave equation**: **v = fλ** (speed = frequency × wavelength) Think of it like this: if a wave completes 50 cycles every second (frequency = 50 Hz), and each cycle is 4 meters long (wavelength = 4 m), then in one second the wave travels: v = 50 Hz × 4 m = **200 m/s** It's that straightforward! The wave covers 50 complete wavelengths per second, so multiply to get total distance per second. ## Why the wrong options tempt you **A) 12.5 m/s** — You divided instead of multiplying (4 ÷ 50 or 50 ÷ 4). The wave equation is multiplication, not division! **B) 54 m/s** — You added them (50 + 4). Addition doesn't work here; we're finding how far the wave travels. **C) 100 m/s** — You might have halved the correct answer by mistake, or used wrong values somewhere. ## Quick takeaway **"Wave speed = frequency × wavelength"** — always multiply these two. If 50 waves pass you every second, each being 4 m long, that's 200 m covered per second!