A cyclist is towing a trailer behind her bicycle - AQA - A-Level Maths Mechanics - Question 15 - 2021 - Paper 2

To find the tension $T$, we need to consider the forces acting on the trailer. Since the cyclist is maintaining a constant speed, the total forces must be balanced, meaning there is no net force acting in the direction of motion. The driving force from the cyclist is 40 N, and the resistance force on the trailer is 12 N.

Using the equation:

$ext{Driving Force} = T + ext{Resistance Force}$

Rearranging gives us:

$T = ext{Driving Force} - ext{Resistance Force}$

Substituting the known values:

$T = 40 N - 12 N = 28 N$

However, this doesn’t match the previously mentioned resistance on the trailer. Since the trailer's resistance is independent, we must adjust, realizing that the balance suggests $T$ must equal 12 N to counteract the forces acting on the trailer. Thus:

$T = 12 N$