A girl runs a 400 m race in a time of 84 s. In a model...

 

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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 ms¹¹. She maintains this speed for 60 s and then moves with constant deceleration for 20 s, crossing the finish line with a speed of V ms¹¹. a) Sketch a speed-time graph for the motion of the girl during the whole race. b) Find the distance run by the girl in the first 64 s of the race. c) Find the value of V. d) Find the deceleration of the girl in the final 20 s of her race. 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 ms¹¹. She maintains this speed for 60 s and then moves with constant deceleration for 20 s, crossing the finish line with a speed of V ms¹¹. a) Sketch a speed-time graph for the motion of the girl during the whole race. b) Find the distance run by the girl in the first 64 s of the race. c) Find the value of V. d) Find the deceleration of the girl in the final 20 s of her race.

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ANSWER a Graph drawn above b Total distance ... View the full answer