Distance speed and acceleration WJEC Physics Unit 2

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Distance, speed and acceleration WJEC Physics Unit 2 - 2. 1 WJEC Science (Double

Distance, speed and acceleration WJEC Physics Unit 2 - 2. 1 WJEC Science (Double Award) Unit 6 - 6. 1

Distance, speed and acceleration Speed = distance (metres) time (seconds) S V× t Click

Distance, speed and acceleration Speed = distance (metres) time (seconds) S V× t Click here for the answers 1) Aled walks 200 m in 40 s. What is his speed? 2) Lowri travels 2 km in 1000 s. What is her speed? 1) 5 m/s 3) How long would it take for Dafydd to run 100 m if he runs at a speed of 10 m/s? 2) 2 m/s 4) Heledd travels at a speed of 50 m/s for 20 s. How far does she travel? 4) 1000 m/s 5) A car travels at a speed of 85 mph (about 40 m/s). How long would it take for him to travel 20 km? 3) 10 s 5) 500 s

Distance-Time Graphs 4) 2) Straight horizontal line = 40 Motionless Straight line at a

Distance-Time Graphs 4) 2) Straight horizontal line = 40 Motionless Straight line at a downwards angle = Constant speed in reverse Distance (metres) 30 20 10 0 Time/s 20 40 1) Straight line at an upwards angle = Constant speed forwards (low) 60 80 100 3) Straight line at a greater angle upwards = Constant speed forwards (high)

40 Distance (m) 30 20 10 0 20 40 60 1) What is the

40 Distance (m) 30 20 10 0 20 40 60 1) What is the speed during the first 20 s? 2) How far is the object from the start after 60 seconds? 3) What is the speed during the last 40 s? 4) When was the object travelling at its fastest? 80 100 Time (s) Click here for the answers 1) 0. 5 m/s 2) 40 m 3) 2 m/s in reverse 4) 40 – 60 s

Speed v Velocity Simply, speed is the distance travelled per second … This car’s

Speed v Velocity Simply, speed is the distance travelled per second … This car’s speed is 20 m/s Velocity is the distance travelled per second in a specific direction …. . Speed of 20 m/s to the right

Acceleration acceleration (m/s 2) = change in velocity (m/s) time (s) V-U a×t 1)

Acceleration acceleration (m/s 2) = change in velocity (m/s) time (s) V-U a×t 1) A biker speeds up from 0 to 10 m/s in 5 s. What is the acceleration? 2) A ball is dropped with an acceleration of 10 m/s 2 for 12 s. By how much will the velocity of the ball change? 3) A car speeds up from 10 to 20 m/s with an acceleration of 2 m/s 2. How much time did this change take? 4) A rocket speeds up from 1 000 m/s to 5 000 m/s in 2 s. What is its velocity? Click here for the answers 1) 2 m/s 2 2) 120 m/s 3) 5 s 4) 2000 m/s 2

Velocity-Time Graphs velocity (m/s) 1) Line at an upwards Constant angle = 80 acceleration

Velocity-Time Graphs velocity (m/s) 1) Line at an upwards Constant angle = 80 acceleration 4) Line at a downwards angle = Constant deceleration 60 40 20 0 t(s) 10 2) Horizontal line = Constant velocity 20 30 40 50 3) Line at an upwards angle = Constant acceleration (lower)

Calculating the Distance 80 Velocity (m/s) 60 40 20 t/s Chapter 15 0 10

Calculating the Distance 80 Velocity (m/s) 60 40 20 t/s Chapter 15 0 10 20 30 40 50 To calculate the total distance of the journey, you must calculate the area under the graph.

80 Velocity (m/s) 60 40 20 t/s 0 10 20 30 1) What is

80 Velocity (m/s) 60 40 20 t/s 0 10 20 30 1) What is the velocity after 10 s? 2) What is the acceleration between 20 a 30 s? 3) What is the deceleration between 30 and 50 s? 4) What was the distance of the journey? 40 50 Click here for the answers 1) 40 m/s 2) 2 m/s 2 3) 3 m/s 2 4) 1700 m

Braking Distances for a car… A car’s braking distance is composed of two elements:

Braking Distances for a car… A car’s braking distance is composed of two elements: Thinking distance 9 m 1) The thinking distance – this is the distance you travel whilst reacting. 2) Braking distance – this is the distance travelled whilst braking. Braking distance 14 m 13 m/s (30 m. p. h. ) 15 m 21 m 22 m/s (50 m. p. h. ) 31 m/s (70 m. p. h. ) 38 m 75 m Total 23 m 53 m 96 m You do not need to learn the above figures for the exam, but they show the car’s speed affect its stopping distance. What else affects a car’s stopping distance?

A Car’s Stopping Distance … High speed Tiredness Drugs Thinking distance Alcohol Impaired vision

A Car’s Stopping Distance … High speed Tiredness Drugs Thinking distance Alcohol Impaired vision Ice on the road Worn tyres or brakes Braking distance Wet road surface High speed

A car’s stopping distance Visit the website below to see video clips on the

A car’s stopping distance Visit the website below to see video clips on the effects of speed, tiredness, alcohol misuse etc. on the stopping distance. http: //think. direct. gov. uk