[PHY] Chapter 2 - Kinematics

DARRELL ER (COPYRIGHTED) TOPIC 2: KINEMATICS DARRELL ER (COPYRIGHTED) ©

CHAPTER ANALYSIS THE ABOUT TIME EXAM WEIGHTAGE DARRELL ER (COPYRIGHTED) ©

TWO PHYSICAL QUANTITIES DISTANCE DISPLACEMENT KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

DISPLACEMENT Unit: m Distance is defined as the total length travelled, regardless of the direction of the motion. Distance is a scalar quantity. A scalar is a physical quantity that has magnitude only. Unit: m 40m 70m 85m Total Displacement: 85 m If a man walk along the same curved path from point A to point B, 40m 70m 85m If a man walk along the curved path from point A to point B, Total Distance: 40m + 70m = 110 m So even though the man had travelled 110m, his displacement is only effectively 85m. DARRELL ER (COPYRIGHTED) ©

TWO PHYSICAL QUANTITIES SPEED VELOCITY KEY CONCEPT DARRELL ER (COPYRIGHTED) ©

VELOCITY ms-1 Speed is defined as the rate of change of distance with respect to time. Speed is a scalar quantity & has no direction. Unit: ms-1 120 m EXAMPLE Amy & David walk towards each other. Taking the direction to the left as positive, Amy’s speed: 100m / 25s = 4 ms-1 Amy’s velocity: 100m / 25s = 4 ms-1 When calculating velocity, always take into account the direction! 100 m Amy, 25s David, 30s David’s speed: 120m / 30s = 4 ms-1 David’s velocity: -120m / 30s = -4 ms-1 DARRELL ER (COPYRIGHTED) ©

AVERAGE SPEED ACCELERATION ADVANCED CONCEPT DARRELL ER (COPYRIGHTED) ©

What is the average speed of the car? Total Distance = Area under graph = (½ x 2 x 10) + (4 x 10) + (½ x 2 x 10) + (½ x 4 x 10) = 80m Average speed = 80m / 12s = 6.67 ms-1 What is the average velocity of the car? Total Displacement = area under graph = (½ x 2 x 10) + (4 x 10) + (½ x 2 x 10) - (½ x 4 x10) = 40m Average velocity = 40m / 12s = 3.33 ms-1 What is the instantaneous speed of the car at 1s? The instantaneous speed of the car at 1s is 5 ms-1 . Average Speed Average speed is the total distance travelled over a period of time. Formula: Average Speed = Total Distance / Total Time Instantaneous speed is the speed at a specific point in time. *Area of graph in negative region is in the reverse direction! DARRELL ER (COPYRIGHTED) ©

What is the acceleration of the car in the first 2 seconds? Acceleration = (v-u) / t = (10-0) / 2 = 5.0 ms-2 What is the acceleration of the car between 2s - 6s? The car is travelling at constant velocity, hence there is no acceleration. Describe what is happening to the car from 6s to 12s. From 6s to 8s, the car starts to decelerate, reducing its velocity from 10ms-1 to 0ms-1. At the 8s mark, the car is at rest momentarily before moving in the opposite direction. As it is reversing, it speeds up to reach -10ms-1. At 10s, the car slows down while traveling in the opposite direction before coming to rest at 12s. Acceleration Acceleration is the rate of change of velocity with respect to time. Formula: Acceleration = Change in velocity / time a = (v-u) / t DARRELL ER (COPYRIGHTED) ©

GRAPHICAL ANALSIS DISPLACEMENT-TIME GRAPH VELOCITY-TIME GRAPH KEY CONCEPT DARRELL ER (COPYRIGHTED) ©