How Do You Determine Force from a Given Trajectory in Physics?

[Physics Help!]

A body of mass m moves under the influence of force F(r). Given it's trayectory r(t), find F(r).

Attempt:
F(t) = M * d^r/dt^2


I don't know what to do after that...

 

[Redbelly98]

A body of mass m moves under the influence of force F(r). Given it's trayectory r(t), find F(r).

Attempt:
F(t) = M * d^r/dt^2


I don't know what to do after that...

That looks like a sufficient answer to me.

 

[ashishsinghal]

Nothing else could really be done.