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Chapter 2: Kinematics. 2.1 Uniform Motion 2.2 Instantaneous Velocity 2.3 Finding Position from Velocity 2.4 Motion with Constant Acceleration 2.5 Free Fall 2.6 Motion on an Inclined Plane 2.7* Instantaneous Acceleration. Stop to think 2.1 P38 Stop to think 2.2 P44 Stop to think 2.3 P48
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Chapter 2: Kinematics • 2.1 Uniform Motion • 2.2 Instantaneous Velocity • 2.3 Finding Position from Velocity • 2.4 Motion with Constant Acceleration • 2.5 Free Fall • 2.6 Motion on an Inclined Plane • 2.7* Instantaneous Acceleration
Stop to think 2.1 P38 Stop to think 2.2 P44 Stop to think 2.3 P48 Stop to think 2.4 P54 Stop to think 2.5 P61 Example 2.3 P 40 Example 2.4 P 41 Example 2.7 P 45 Example 2.10 P 47 Example 2.14 P 53 Example 2.16 P 56 Example 2.18 P 58
Motion in one dimension • Determining the signs of position, velocity and acceleration
Motion along a straight line Can be illustrated by position-versus-time graph: 4 s 1 s 2 s 3 s x Continuous (smooth) curve Origin (x=0) x 10 cm 20 cm 70 cm 40 cm 2 3 1 4 t(s)
Interpreting a position graph 1.What is the position at t =0min 2.What is the position at t =30min 3.What is the velocity at t = 20min 4.What is the velocity at t = 50min 5. What is the acceleration at t=20min 6. If this is V vs. t graph, and x = 0 km at t = 0min. What is the position at t = 80 min
Uniform Motion • V(avg)= comstant • The position-vs-graph is a straight line • Vs = ∆s/ ∆t • Sf = Si + Vs ∆t
Instantaneous velocity • Using motion diagrams and graphs
Stop to think 2.2Which velocity-versus-time goes with the position –versus-time graph C
Relating a velocity graph to a position graph The value of the velocity at Any time equals the slope of The position graph T
Using calculus to find the velocity Ex. A particle’s position is given by the function 1.What is particle’s position at t = 2s? x = -8+6 = -2 m 2. What is the velocity at t = 2s V|t=2 = -3(2)2+3=-9 m/s
Example 2.9 1.Where is particle’s turning point? 2.At what time does the particle reach the origin?
Motion with constant acceleration Definition of acceleration If set t0=0s, ∆t = t See page 57
Example 2.13A rocket sled accelerates at 50m/s2 for 5.0 s. Coasts for 3.0 s, then deploys a parachute and decelerates at 3.0m/s2 until coming to a halt. What is the maximum velocity of the rocket sled? What is the total distance traveled?
The apple and feather in this photograph are falling in a vacuum Two objects dropped from the same height will, if air resistance can be neglected Hit the ground at the same time and with the same speed
Free Fall g = 9.8m/s2 If we choose the y-axis to point vertically up
Example 2.16 A falling rockA rock is released from rest at the top of 100-m-tall building.How long does the rock take to fall to the ground, what is impact velocity? • Y0=100m Y1=0m • Vy0= 0 m/s t0 = 0 s
Homework 2.50 • A 1000Kg weather rocket is launched straight up. The rocket motor provides a constant acceleration for 16s, then the motor stops. The rocket altitude 20 s after launch is 5100m. You can ignore the air resistance a) What was the rocket’s acceleration during the first 16 s. The rocket launched with Vo = 0, after 16 s b) After motor stops, the acceleration is –g as free fall. c) The rocket’s speed as it passes through a cloud 5100m above the ground
Quiz questions:Two stones are release from rest at certain height one after the other • A) Will the difference in their speed increase, decrease or stay the same B) Will their separation distance increase, decrease or stay the same