Pure Core 1 June 2025, Question 9 9 marks
A pendulum comprises an object P of mass m kg and a string of length 7 m. One end of the string is attached to P and the other end is attached to a fixed point A.
At time t seconds, t ⩾ 0, the string forms an angle of θ radians, measured anti-clockwise, from the downward vertical through A, as shown in the diagram.
When t = 0, θ = θ0 > 0 and P is released from rest. You may assume that in the subsequent motion P moves along the arc of a circle, centre A and radius 7 m, and that |θ| ⩽ θ0 for all t ⩾ 0.
The motion of P is modelled by the following differential equation.
In some situations, it is appropriate to approximate (∗) with the following differential equation.
Reveal mark scheme
Reveal mark scheme
An additional force now acts on P. It can be shown that it is now appropriate to model the motion of P with the differential equation +
+
= 0 where k > 0.
Find the range of values of m, in terms of k, for which the motion of the pendulum is
overdamped.
Reveal mark scheme