The displacement s s\,s metres of a particle from a fixed point after t t\,t seconds is modelled, for 0≤t≤60\leq t\leq 60≤t≤6, by s=ut+12at2s=ut+\dfrac12at^2s=ut+21at2, where u=4 m s−1u=4\text{ m s}^{-1}u=4 m s−1 and a=3 m s−2a=3\text{ m s}^{-2}a=3 m s−2.
Explain why both terms on the right-hand side have the unit metre.
Find the average speed of the particle during the six seconds.