Complete the sentences to explain why an object falling vertically at terminal velocity remains at a constant speed:

"An object falling vertically through a fluid at terminal velocity maintains a constant speed because the downward force, caused by ________, is balanced by the upward resistive force, caused by ________."

Write down the equation that links distance travelled ($s$), constant speed ($v$), and time taken ($t$).

The distance between an earthquake epicentre and a seismic recording station is $1.08\times 10^{6}m$. A primary seismic wave (P-wave) travels through the Earth's crust at a constant speed of $6.0\times 10^{3}m/s$. Calculate the time taken for the P-wave to travel from the epicentre to the recording station.