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)|
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:
Force can be estimated using the equation:
force = mass × acceleration
This is when:
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
Estimate the force needed to accelerate a lorry to its top speed on a single carriageway, using the values given above.
Force (N) = mass (kg) × acceleration (m/s2)
Force = 36,000 × 0.4
Force = ~14,400 N