A particle of mass M is constrained to move in a vertical plane along a trajectory given by X = Acos(θ) and Y = Asin(θ), where A is constant. The Lagrangian function can be given as (Hint: take V=0 at Y=0). Take two generalized coordinates (r, θ):
r = A*cos(θ)
z = A*sin(θ)
The Lagrangian function is:
L = T - V
where T is the kinetic energy and V is the potential energy. The kinetic energy T can be expressed as:
T = (1/2)*M*(ṙ^2 + (r^2)*(θ̇^2))
where ṙ and θ̇ are the time derivatives of r and θ, respectively.
The potential energy V can be expressed as:
V = -M*g*z
where g is the acceleration due to gravity.
Therefore, the Lagrangian function L can be written as:
L = (1/2)*M*(ṙ^2 + (r^2)*(θ̇^2)) + M*g*A*sin(θ)