Calculating Speed and Acceleration BUTTONS Click here Clicking

Calculating Speed and Acceleration BUTTONS Click here: Clicking here will move you the page. Clicking here will here bring reveal will reveal some back an information. to answer. a next this page. Clicking here on. Clicking will me will take will allow take you you totoayou to hear list SIback ofto multipliers some equations, information table. clicking Clicking on the here topic. here again Clicking again will here take return you again back you willto to stop your thethe previous sound. page. TOPICS Jump to… …speed and how to calculate it (two pages). Jump to… …the difference between speed and velocity (one page). Jump to… …acceleration and how to calculate it (two pages). …practice questions (three pages). Jump to… …exam questions (four pages).

Speed is defined as: “…the distance travelled per unit of time…” On our roads we see speed cameras. e. g. 1 m/s Click the green icons for more information Time between the two pictures is 0. 25 seconds 5 m/s These measure how fast speeding cars travel. Distance of 1 m in a time of 1 s Click here to see how the camera works speed = 7 = 28 m/s 0. 25 Distance of 5 m in a time of 1 s Camera Click the correct answer from the list 7 m of 2 s? Distance of 12 m in a time Distance between each line is 1 m 12 m/s White marks 6 m/s 24 m/s

Calculating Speed We can use an equation to calculate speed. Click on the distance and time terms to see other ways of writing the equation speed = distance time Click here for more information distance = speed x time distance = 100 m time = 5 s speed = ? Calculations Step 1 Choose the equation Step 2 Numbers Step 3 Answer with a unit Higher Tier only time = distance speed = distance time speed = 100 m 5 s speed = 20 m/s

Speed and Velocity Speed is an example of a “scalar” measurement. Scalars have a value only and are therefore always positive. Velocity is an example of a “vector” measurement. Vectors have value and direction and may therefore be positive or negative depending on their direction of motion. Speed = 5 m/s Velocity = +5 m/s Speed = 5 m/s Velocity = -5 m/s Effect of direction - Left is negative Right is positive +

Acceleration tells us how an objects velocity changes. Click the red word in each example for more information If an object moves with constant velocity it’s acceleration iszero. Start = 20 m/s Finish = 20 m/s When an object’s velocity is increasing we say it isaccelerating. Start = 0 m/s Finish = 20 m/s When an object’s velocity is decreasing we say it isdecelerating. Start = 20 m/s Finish = 0 m/s

Calculating Acceleration We can use an equation to calculate acceleration. Click on a term to show other forms of the equation. a = Δv t acceleration = Change in velocity time Δv = a x t t = Δv a Higher Tier only Change in velocity = final – initial 15 m/s to 0 m/s in 3 s 4 m/s to 20 m/s in 4 s Click on a vehicle to see it’s acceleration. a = Δv t a = 20 -4 4 a = 4 m/s 2 Why is the answer minus? a = Δv t a = 0 -15 3 a = -5 m/s 2

Practice Question 1 a) The truck travels 2000 m in 125 s. Us an equation from the equation list to calculate the speed of the truck. speed = distance time speed = 2000 125 speed = 16 m/s Higher Tier Only b) If the truck now continues at the same speed for an extra 40 seconds, what will be the total distance travelled? (HINT – You’ll have to rearrange the above equation). distance = speed x time distance = 16 x 40 distance = 640 m + 2000 m distance = 2640 m

Practice Question 2 a) What is the acceleration of a racing car if it accelerates from being stationary to 36 m/s in 3 seconds? a = Δv t a = 36 -0 3 Higher Tier Only a = 12 m/s 2 b) How long will it take for the car to reach 100 m/s if it continues to accelerate at the same rate? (HINT – You’ll have to rearrange the above equation). t = Δv a t = 100 -0 12 t = 8. 33 s

Practice Quiz Click the correct answer for each vehicle. speed = distance 6 m/s time distance = 56 m time = 8 s speed = ? change in velocity, Δv = 72 m/s time = 4. 5 s acceleration = ? 7 m/s speed = 56 m 8 s 8 m/s speed = 7 m/s 14 m/s 2 15 m/s 2 16 m/s 2 Higher Tier only speed = 24 m/s 0. 125 s time = ? 100 s distance = 3 km 125 s a = Δv t a = 72 -0 m/s 4. 5 s a = 16 m/s 2 time = distance speed time = 3000 m 24 s time = 125 s

Exam Question 1 WJEC Physics 2 June 2014 (Foundation) Q 4 There are 4 gaps worth 0. 5 s each The ball has passed 9 marks, with each mark worth 1 m 9 x 1 9 0. 5 x 4 2

speed = 9 2 4. 5 Distance between the balls is increasing. The distance between the balls would be less.

Exam Question 2 WJEC Physics 2 January 2014 (Higher) Q 1 a = Δv t a = 0 -15 5 = -3 3 Mean speed= 15 + 0 2 7. 5

EQUATIONS er h hig r e igh h h r e h g i r e igh h Open the file “Maths for Physics” for more about the use of mathematics in Physics.

SI MULTIPLIERS p - pico k - kilo n - nano M - mega - micro G - giga m - milli T - tera You only see the letter of the prefix on an exam paper, NOT the name. On a Foundation paper only milli, kilo and mega are used.