Final answer:
The actual speed of a car if the speedometer reads 65mph may not exactly coincide due to factors such as speedometer calibration errors, tire wear, and changes in tire pressure. Road conditions and tire size can also introduce variation.
Step-by-step explanation:
The actual speed of a car if the speedometer reads 65mph can vary due to a number of factors, including speedometer calibration, tire wear, and tire pressure. Speedometers can have an uncertainty, which means they might not be 100% accurate. For example, if a speedometer has a 5.0% uncertainty, the actual speed of the car could be 5% higher or lower than what is displayed.
Considering the condition of the tires and road, if a tire is worn out or under-inflated, it might be smaller in diameter, which could lead to showing a higher speed than the vehicle's actual speed. Conversely, over-inflation or larger tires might cause the speedometer to read lower than the car's actual speed. Road conditions such as inclines and declines can also cause slight variations in speed due to the change in resistance against the car.
If a car's speedometer has an uncertainty of 2.0 km/h at a speed of 90 km/h, the percent uncertainty is calculated by dividing the uncertainty by the reading and then multiplying by 100, resulting in a value of approximately 2.2%. If that same percent uncertainty applies at 60 km/h, the range of speeds could also be calculated considering this uncertainty.