Ch.7 Equations of Motion ( 運動方程式 ) 1. 2 7.1 Equations of Motion.

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1 Ch.7 Equations of Motion ( 運動方程式 ) 1

2 2 7.1 Equations of Motion

3 3 symbol ( 符號 ) physical quantity ( 物理量 ) unit ( 單位 ) s displacement ( 位移 ) m u initial velocity ( 最初速度 ) ms -1 v final velocity ( 最後速度 ) ms -1 t time ( 時間 ) s a acceleration ( 加速度 ) ms -2

4 4 Class Exercise 7.1 A ball moves down a slope with an initial velocity of 5 ms -1. The acceleration of the ball is 2 ms -2. What is the velocity of the ball 3 s later?

5 5 Class Exercise 7.1 A ball moves down a slope with an initial velocity of 5 ms -1. The acceleration of the ball is 2 ms -2. What is the velocity of the ball 3 s later? 5 3 2

6 6

7 7 v = 5 + (2)(3) = 11 ms -1

8 8 Class Exercise 7.2 A car starting from rest accelerates at 4.0 ms -2 for 10 s. Calculate the distance travelled by the car during this time.

9 9 Class Exercise 7.2 A car starting from rest accelerates at 4.0 ms -2 for 10 s. Calculate the distance travelled by the car during this time. 0 10 4

10

11 11 s = (0)(10) + (0.5)(4)(10) 2 = 200 m

12 12 Class Exercise 7.3 The driver of a lorry applies brakes to stop the lorry from initial velocity of 20 ms -1. The deceleration of the lorry is 5 ms -2. What is the stopping distance of the lorry?

13 13 Class Exercise 7.3 The driver of a lorry applies brakes to stop the lorry from initial velocity of 20 ms -1. The deceleration of the lorry is 5 ms -2. What is the stopping distance of the lorry? 20 0

14 14

15 15 (0) 2 = (20) 2 + (2)(-5)(s) 10s = 400 s = 40 m

16 16 Class Exercise 7.4 Peter is running with uniform acceleration along a straight road. At time t = 0, his velocity is 1.2 ms -1. After 6 s, his velocity becomes 2.4 ms -1. (a) Calculate his acceleration.

17 17 Class Exercise 7.4 Peter is running with uniform acceleration along a straight road. At time t = 0, his velocity is 1.2 ms -1. After 6 s, his velocity becomes 2.4 ms -1. (a) Calculate his acceleration. u = 1.2 ms -1 t = 6 s v = 2.4 ms -1

18 18 Class Exercise 7.4 Peter is running with uniform acceleration along a straight road. At time t = 0, his velocity is 1.2 ms -1. After 6 s, his velocity becomes 2.4 ms -1. (a) Calculate his acceleration. u = 1.2 ms -1 t = 6 s v = 2.4 ms -1 v = u + at 2.4 = 1.2 + (a)(6) a = 0.2 ms -2

19 19 (b) Calculate the distance traveled in this 6 s.

20 20 (b) Calculate the distance traveled in this 6 s. v 2 = u 2 + 2as (2.4) 2 = (1.2) 2 + 2(0.2)(s) s = 10.8 m OR s = ut + (0.5)at 2 = (1.2)(6) + (0.5)(0.2)(6) 2 s = 10.8 m

21 21 Class Exercise 7.5 A car is moving with uniform deceleration along a straight road. Its velocity decreases from 20 ms -1 to 10 ms -1` after travelling a distance of 50 m. (a) What is its deceleration?

22 22 Class Exercise 7.5 A car is moving with uniform deceleration along a straight road. Its velocity decreases from 20 ms -1 to 10 ms -1` after travelling a distance of 50 m. (a) What is its deceleration? u = 20 ms -1 s = 50 m v = 2.4 ms -1

23 23 Class Exercise 7.5 A car is moving with uniform deceleration along a straight road. Its velocity decreases from 20 ms -1 to 10 ms -1` after travelling a distance of 50 m. (a) What is its deceleration? u = 20 ms -1 s = 50 m v = 2.4 ms -1 v 2 = u 2 + 2as (10) 2 = (20) 2 + 2(a)(50) a = -3 ms -2

24 24 (b) How much further distance will the car travel before it comes to rest?

25 25 (b) How much further distance will the car travel before it comes to rest? v 2 = u 2 + 2as (0) 2 = (10) 2 + 2(-3)(s) 6s = 100 s = 16.7 m u = 10 ms -1 a = -3 ms -2 v = 0

26 26 Homework: Assignment Book 1. Chapter 7: equations of Motion Q.1 – Q.7 (p.26-33) 2. Deadline: 2009 - ___ - ____