The remote control transmits radio waves to the car aerial - AQA - GCSE Physics - Question 6 - 2020 - Paper 1

When the car aerial absorbs radio waves, an alternating current is induced in the electrical circuit. This current oscillates with the same frequency as the radio waves, allowing the circuit to process the signals.

1. Radio waves are transverse waves, while sound waves are longitudinal waves.
2. Radio waves travel at the speed of light, while sound waves travel through a medium and are much slower.

The car is accelerating continuously during the first 30 seconds.

To find the speed ($v$) after 20 seconds, we can use the average speed formula if acceleration is constant. Assuming constant acceleration of $0.28$ m/s² from earlier calculations, we get:

$v = u + at$ With initial speed ($u$) = 0 m/s: $v = 0 + (0.28 m/s²)(20 s) = 5.6 \, m/s$

Thus, the speed of the car after 20 seconds is 5.6 m/s.

Using Newton's second law, the resultant force ($F$) can be calculated using:

$F = ma$

First, calculate mass ($m$) given:

• Initial speed ($u$) = 0.12 m/s
• Final speed ($v$) = 0.52 m/s
• Acceleration ($a$) = 0.040 m/s²

Work done ($W$) is given as 0.48 J, so:

Using the work-energy principle: $W = F \cdot d$

displacement ($d$) can be calculated: $d \approx \frac{(0.12 + 0.52)}{2} \cdot t = \frac{0.64 m/s}{2} \cdot 10 s = 3.2 m \implies F = \frac{0.48 J}{3.2 m} = 0.15 \text{ N}$

Thus, the resultant force needed is 0.15 N.

The car has a maximum speed because the driving force provided by the motor is balanced by the resistance forces such as air resistance. As the car accelerates, these resisting forces increase until they equal the driving force, at which point the car can no longer accelerate and travels at its maximum speed (terminal velocity).