• Acceleration?is defined as the?rate of change of velocity
  • In other words, it describes how much an object's velocity?changes?every?second
• The equation below is used to calculate the average acceleration of an object:

• Where:
  • a?= acceleration in metres per second squared (m s^–2)
  • Δv?= change in velocity in metres per second (m s^–1)
  • t?= time taken in seconds (s)

• The?change in velocity?is found by the?difference?between the initial and final velocity, as written below:

change in velocity = final velocity ? initial velocity

Equations linking displacement, velocity, and acceleration

Speeding Up and Slowing Down

• An object that speeds up is?accelerating
• An object that slows down is?decelerating
• The?acceleration?of an object can be?positive?or?negative, depending on whether the object is speeding up or slowing down
  • If an object is?speeding up, its acceleration is?positive
  • If an object is?slowing down, its acceleration is?negative?(sometimes called?deceleration)

A rocket speeding up (accelerating) and a car slowing down (decelerating)

Part (a)

Step 1: List the known quantities

• • Initial velocity = 50 m s^–1
  • Final velocity = 42 m s^–1

Step 2: Write the relevant equation

change in velocity = final velocity ? initial velocity

Step 3: Substitute values for final and initial velocity

change in velocity = 42 ? 50 = ?8 m s^–1

Part (b)

Step 1: List the known quantities

• • Change in velocity, Δv?= ?8 m s^–1
  • Time taken,?t?= 30 s

Step 2: Write the relevant equation

Step 3: Substitute the values for change in velocity and time

a?= ?8 ÷ 30 = ?0.27 m s^–1

Step 4: Interpret the value for deceleration

• • The answer is?negative, which indicates the train is?slowing down