Solution = 15 v = 0 u = ? a = s = 5 t Use 15 = 0 + 5 a a = 3 m s-2 v = u + at = u + at = 0 v = 15 u = ? a = s = 3 t Use 0 = 15 + 3 a a = -5 m s-2 v = u + at distance = area of first triangle + area of middle rectangle + area of second triangle = ½ (5)(15) + (20)(15) + ½ (3)(15) = 37.5 + 300 + 22.5 = 360 m = v = 15 u = 3 a = 13.5 s = t Use = 0 + 2(3)(13.5) = 81 m = 9 m s-1 v2 = u2 + 2as v2 v 2012 OL A car travels a straight level road. It passes a point with a speed of 8 m s−1 and accelerates uniformly for 12 seconds to a speed of 32 m s−1. P It then travels at a constant speed of 32 m s−1 for 7 seconds. Finally the car decelerates uniformly from 32 m s−1 to rest at a point Q. The car travels 128 metres while decelerating. Find the acceleration the deceleration the distance from to P Q speed of the car when it is 72 m from {this last part is quite tricky see how you get on} Q – Solution Begin by drawing a velocity-time graph to represent the motion Note that the initial velocity here is not 0. v = u + at 32 = 8 + a(12) = 2 m s-2 a
Solution v = 15 u = 0 a = ? s = t = 5 Use v = u + at 15 = 0 + 5 a a = 3 m s-2 = u + at v = 0 u = 15 a = ? s = t = 3 Use v = u + at 0 = 15 + 3 a a = -5 m s-2 distance = area of first triangle + area of middle rectangle + area of second triangle = ½ (5)(15) + (20)(15) + ½ (3)(15) = 37.5 + 300 + 22.5 = 360 m v = u = 15 a = 3 s = 13.5 t = Use v2 = u2 + 2as = 0 + 2(3)(13.5) v2 = 81 m v = 9 m s-1 2012 OL A car travels a straight level road. It passes a point P with a speed of 8 m s−1 and accelerates uniformly for 12 seconds to a speed of 32 m s−1. It then travels at a constant speed of 32 m s−1 for 7 seconds. Finally the car decelerates uniformly from 32 m s−1 to rest at a point Q. The car travels 128 metres while decelerating. Find the acceleration the deceleration the distance from P to Q speed of the car when it is 72 m from Q {this last part is quite tricky – see how you get on} Solution Begin by drawing a velocity-time graph to represent the motion Note that the initial velocity here is not 0. v = u + at 32 = 8 + a(12) a = 2 m s-2
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