The graph shows how the velocity of a small car changes with time - Edexcel - GCSE Physics - Question 3 - 2013 - Paper 1

The estimated velocity of the car at three seconds is 10 m/s.

To calculate the acceleration, use the formula:

a = \frac{10 - 0}{4} = 2.5 , \text{m/s}^2$$

Acceleration is defined as the rate of change of velocity over time. Since velocity is measured in meters per second (m/s) and time is measured in seconds (s), when we calculate acceleration, the dimensions become:

$ext{units of acceleration} = \frac{\text{units of velocity}}{\text{units of time}} = \frac{\text{m/s}}{\text{s}} = \text{m/s}^2$

When the car is moving at a constant velocity (10 m/s) for a period of 6 seconds:

Distance traveled = velocity × time = 10 m/s × 6 s = 60 m.

When the car is slowing down from 20 m/s to 0 m/s over a duration, the average speed during this time is:

$\text{Average velocity} = \frac{20 + 0}{2} = 10 \, \text{m/s}$

If the car takes 2 seconds to stop (which means accelerating negatively), then:

Distance = average velocity × time = 10 m/s × 2 s = 20 m.

Thus, the car travels 60 m at a constant velocity compared to only 20 m while slowing down, proving that it travels further at a constant velocity.