A girl runs a 400 m race in a time of 84 s . In a model of this race, it is assumed that, starting from rest, she moves with constant acceleration for 4 s , reaching a speed of \(5 \mathrm {~m} \mathrm {~s} ^ { - 1 }\). She maintains this speed for 60 s and then moves with constant deceleration for 20 s , crossing the finishing line with a speed of \(V \mathrm {~m} \mathrm {~s} ^ { - 1 }\).
Sketch, in the space below, a speed-time graph for the motion of the girl during the whole race.
Find the distance run by the girl in the first 64 s of the race.
Find the value of \(V\).
Find the deceleration of the girl in the final 20 s of her race.