It is important to be able to estimate speeds, accelerations and forces involved in road vehicles. The symbol ~ is used to indicate that a value or answer is approximate. The table gives some examples.
Vehicle
Maximum legal speed on a single carriageway (m/s)
Mass (kg)
Acceleration (m/s²)
Family car
~27
~1,600
~3
Lorry
~22
~36,000
~0.4
Vehicle
Family car
Maximum legal speed on a single carriageway (m/s)
~27
Mass (kg)
~1,600
Acceleration (m/s²)
~3
Vehicle
Lorry
Maximum legal speed on a single carriageway (m/s)
~22
Mass (kg)
~36,000
Acceleration (m/s²)
~0.4
Estimating acceleration
It takes a cyclist approximately 12 s to reach a top velocity of 7.5 m/s. To estimate the cyclist's acceleration, use the formula:
acceleration is measured in metres per second squared (m/s2)
For example, to estimate the force needed to accelerate a family car to its top speed on a single carriageway, use the approximate values given above of ~1,600 kg for the mass of the car and ~3 m/s2 for the acceleration.
Force = 1,600 × 3
Force = ~4,800 N
Question
Estimate the force needed to accelerate a lorry to its top speed on a single carriageway, using the values given above.
