Two balls A A\,A and B B\,B have mass of 3 kg and 2 kg respectively. The balls are connected by a string which passes over a fixed pulley. Ball A A\,A is held at rest with the string taut and the hanging parts of the string vertical. Ball A A\,A is released. The string is modelled as being light and inextensible, the balls are modelled as particles, the pulley is modelled as being smooth and air resistance is ignored.

Using the model, find, in terms of ggg, the magnitude of the force exerted on the pulley by the string while A A\,A is falling and before B B\,B hits the pulley.
State one limitation of the model, apart from ignoring air resistance, that will affect the accuracy of your answer to part (a).
30 exam-style questions on Edexcel AS Level Maths Forces and Motion, covering 10.1 Force Diagrams, 10.2 Forces as Vectors, 10.3 Forces and Acceleration, 10.4 Motion in 2 Dimensions, 10.5 Connected Particles, and 10.6 Pulleys. Each one has a worked solution and a mark scheme showing where the marks go.