Velocity

Velocity measures how much the displacement changes, every second.

It measures the rate of change of displacement in a specific direction, so it is a vector quantity.

Example

• We walk 25km north in 5 hours, so to find our velocity:

• displacement = 25km north

• velocity = displacement / time

• v=25km\div5h=5kmh^{-1}

• Or, if we walk 400m north then 500m south in 200s, finding our velocity:

• displacement = 400m-500m=100m south

• v=s\div t

• v=100m\div200s=0.5ms^{-1} south

\text{velocity}=\text{displacement}\div\text{time}

s=vt

v=\frac st

Where:

• s is the displacement, measured in metres, m
• v is the velocity, measured in metres per second, ms^{-1} (m/s)
• t is the time, measured in seconds, s

This calculates the average velocity.

A van drives 200m in 10s. Calculate the velocity.

• v=\frac st
• v=\frac{200}{10}=20
• Answer: 20ms^{-1}

A car drives 75m in 5s. Calculate the velocity.

• v=\frac st
• v=\frac{75}{5}=15
• Answer: 15ms^{-1}

A car drives south 50m then north 150m, in 20s. Calculate the average velocity.

• displacement = 150m-50m=100m north
• v=\frac st
• v=\frac{100}{20}=5
• Answer: 5ms^{-1} north

A bike drives 10m in 20s. Calculate the velocity.

• v=\frac st
• v=\frac{10}{20}=0.5
• Answer: 0.5ms^{-1}

A truck drives 240m in 8s. Calculate the velocity.

• v=\frac st
• v=\frac{240}{8}=30
• Answer: 30ms^{-1}

A car drives 300m in 12s. Calculate the velocity.

• v=\frac st
• v=\frac{300}{12}=25
• Answer: 25ms^{-1}

A van drives 600m in 15s. Calculate the velocity.

• v=\frac st
• v=\frac{600}{15}=40
• Answer: 40ms^{-1}

A person cycles for 4h until reaching a destination 100km away. Calculate their average velocity.

• v=\frac st
• v=\frac{100}{4}=25
• Answer: 25kmh^{-1}

A person cycles 100km north in 4h. Calculate their average velocity.

• v=\frac st
• v=\frac{100}{4}=25
• Answer: 25kmh^{-1} north

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