7 A particle \(P\) moves in a straight line. The velocity \(v \mathrm {~m} \mathrm {~s} ^ { - 1 }\) at time \(t\) seconds is given by $$\begin{array} { l l } v = 0.5 t & \text { for } 0 \leqslant t \leqslant 10
v = 0.25 t ^ { 2 } - 8 t + 60 & \text { for } 10 \leqslant t \leqslant 20 \end{array}$$

1. Show that there is an instantaneous change in the acceleration of the particle at \(t = 10\).
2. Find the total distance covered by \(P\) in the interval \(0 \leqslant t \leqslant 20\).
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