5 (a) 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 (a) is calculated using the formula:

a = rac{change ext{ } in ext{ } velocity}{time} = rac{Δv}{Δt}

Given that the change in velocity (Δv) is 8 m/s and the time interval (Δt) is 5 s:

a = rac{8 ext{ m/s}}{5 ext{ s}} = 1.6 ext{ m/s}^2$$

Between 10 s and 15 s, the velocity of the car remains constant at 8 m/s, indicating that the acceleration is 0 m/s². Using Newton's second law:

$$F = m imes a,$$

where m is the mass of the car (assumed here as 1200 kg). Therefore, the resultant force (F) is:

F = 1200 ext{ kg} imes 0 ext{ m/s}^2 = 0 ext{ N}$$