An electric car is travelling at a speed of 16.0 m/s - Edexcel - GCSE Physics - Question 8 - 2023 - Paper 2

Given the average power transfer rate is 17.5 kW (or 17500 W) and the energy transferred is 126 MJ (or 126000000 J), we can use the formula: $t = \frac{E}{P}$ Substituting: $t = \frac{126000000}{17500}$ Calculating: $t \approx 7200 \text{ seconds} = 2 ext{ hours}$ So, the time taken for the battery to become discharged is 2 hours.

The electrical device functions both as a motor when accelerating and as a dynamo when decelerating. When the car decelerates, the energy that would otherwise be wasted during braking is converted back into electrical energy and stored in the battery. This process recharges the battery, thereby increasing the overall efficiency of energy usage and allowing the car to drive longer before the battery gets discharged. Hence, the energy management improves the range of the vehicle.

To evaluate the claim that 126 MJ can be transferred in less than 6 hours, we first calculate the time using the formula: $t = \frac{E}{I \times V}$ Where:

• $E = 126 \times 10^{6} \text{ J}$
• $I = 15.0 \text{ A}$
• $V = 400 \text{ V}$ Substituting values: $t = \frac{126 \times 10^{6}}{15 \times 400}$ Calculating: $t = \frac{126 \times 10^{6}}{6000} = 21000 ext{ s} = 5.83 ext{ hours}$ Since 5.83 hours is less than 6 hours, the claim is justified.

Using the equation: $E = Q \times V$ Rearranging gives: $Q = \frac{E}{V}$ Substituting the values: $Q = \frac{126 \times 10^{6}}{400}$ Calculating: $Q = 315000 \text{ C}$ Therefore, the total charge that moves into the battery is 315,000 C.