5 A child is running up and down a path. A simplified model of the child's motion is as follows:
- he first runs north for 5 s at \(4 \mathrm {~m} \mathrm {~s} ^ { - 1 }\);
- he then suddenly stops and waits for 8 s ;
- finally he runs in the opposite direction for 7 s at \(3.5 \mathrm {~m} \mathrm {~s} ^ { - 1 }\).
- Taking north to be the positive direction, sketch a velocity-time graph for this model of the child's motion.
Using this model,
calculate the total distance travelled by the child,find his final displacement from his original position.