Here is the velocity-time graph for a car for the first 20 s of a journey - Edexcel - GCSE Physics - Question 5 - 2013 - Paper 1

Acceleration can be calculated using the formula:

$\text{Acceleration} = \frac{\text{Change in velocity}}{\text{Time}}$

From part (i), the change in velocity is 8 m/s, and the time interval is 5 s:

$\text{Acceleration} = \frac{8 \text{ m/s}}{5 \text{ s}} = 1.6 \text{ m/s}^2.$

Between 10 s and 15 s, the velocity of the car is constant at 8 m/s. Since there is no change in velocity during this time, the acceleration is zero. Using Newton's second law:

$F = ma$

Where:

• F is the resultant force,
• m is the mass of the car (1200 kg),
• a is the acceleration (0 m/s²).

Thus, we have:

$F = 1200 \text{ kg} \times 0 \text{ m/s}^2 = 0 \text{ N}.$