A car is initially at rest. The table gives the speedometer readings at intervals of every $10\,\text{s}$. Time / s: $0,\,10,\,20,\,30,\,40,\,50,\,60$ Speed / $\text{m s}^{-1}$: $0,\,4,\,8,\,12,\,12,\,12,\,12$ Which row gives the car’s motion during the first $30\,\text{s}$ and during the last $30\,\text{s}$?
- Anon-zero acceleration; at rest
- Bzero acceleration; constant speed
- Czero acceleration; at rest
- Dnon-zero acceleration; constant speed