Sound travels through air at 340 m/s. One steady tone makes waves 2 m long. How many waves pass each second?
Both numbers, the 340 m/s and the 2 m, live inside v = fλ. This time the unknown is f.
Write down what is known: v = 340 m/s, λ = 2 m, f = ?
Write down the equation: v = fλ.
Substitute and calculate: f = 340 ÷ 2 = 170. The frequency is 170 Hz.
Sense check: 170 waves pass each second, each one 2 m from the last, and 170 × 2 = 340, the speed given.
The equation never changes; only the subject moves. Read the question for its unknown, then pick the arrangement where that unknown stands alone.
Sound travels through air at 340 m/s, and a tone's waves are 2 m long. Calculate the frequency.
Write down the values:
v = 340 m/s, λ = 2 m, f = ?
Write down the equation:
v = fλ
Make f the subject:
f = v ÷ λ
Substitute in the values, and calculate:
f = 340 ÷ 2 = 170
The frequency is 170 Hz.
Waves on a lake travel at 12 m/s, with neighboring crests 1.5 m apart. Calculate the frequency.
Write down the values:
v = 12 m/s, λ = 1.5 m, f = ?
Write down the equation:
v = fλ
Make f the subject:
f = v ÷ λ
Substitute in the values, and calculate:
f = 12 ÷ 1.5 = 8
The frequency is 8 Hz.
Waves travel along a cord at 18 m/s, with neighboring crests 2.5 m apart. Enter the frequency, in Hz.
Ripples cross a tray of water at 0.36 m/s, with crests 0.09 m apart. Enter the frequency, in Hz.
A wave machine's waves travel at 15 m/s along a cable, with wavelength 0.6 m. Enter the frequency, in Hz.
Sound travels through ocean water at 1500 m/s. A whale's call makes waves 3 m long. Enter the call's frequency, in Hz.
Griet's ripples cross a shallow pan at 0.8 m/s, with neighboring crests 0.05 m apart. Enter the frequency, in Hz.
A loudspeaker's tone travels through air at 340 m/s, making waves 0.85 m long. Enter the tone's frequency, in Hz.