Recall and use the equation average speed = total distance travelled / total time taken

Cambridge IGCSE Physics 0625 – 1.2 Motion

Objective

Recall and use the equation for average speed: the total distance travelled divided by the total time taken.

Key Concepts

• Distance is a scalar quantity measured in metres (m).
• Time is a scalar quantity measured in seconds (s).
• Average speed is a scalar quantity expressed in metres per second (m s⁻¹).
• The equation applies to any motion where the total distance and total time are known, regardless of changes in speed during the journey.

Equation

The average speed is given by:

\$v_{\text{avg}} = \dfrac{D}{t}\$

where D is the total distance travelled and t is the total time taken.

Step‑by‑Step Procedure

1. Identify the total distance D travelled. Ensure the unit is metres.
2. Identify the total time t taken. Ensure the unit is seconds.
3. Insert the values into the equation \$v_{\text{avg}} = \dfrac{D}{t}\$.
4. Perform the division to obtain the average speed.
5. Check the units: metres ÷ seconds = metres per second (m s⁻¹).

Examples

Practice Problems

1. A cyclist travels a total distance of 180 m in 45 s. Calculate the average speed.
2. A bus covers 500 m in 125 s. What is its average speed?
3. A train travels 720 m in 180 s. Determine the average speed.
4. Solution:
   

   1. \$v_{\text{avg}} = \dfrac{180}{45} = 4\$ m s⁻¹
   2. \$v_{\text{avg}} = \dfrac{500}{125} = 4\$ m s⁻¹
   3. \$v_{\text{avg}} = \dfrac{720}{180} = 4\$ m s⁻¹

Suggested Diagram