Of
Q(3m)
P (4m)
Figure 1
One end of a string is attached to a small ball P of mass 4m.
The other end of the string is attached to another small ball Q of mass 3m.
The string passes over a fixed pulley.
Ball P is held at rest with the string taut and the hanging parts of the string vertical, as
shown in Figure 1.
Ball P 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.
(a) Using the model, find, in terms of m and g, the magnitude of the force exerted on the
pulley by the string while P is falling and before Q hits the pulley.
(b) State one limitation of the model, apart from ignoring air resistance, that will affect
the accuracy of your answer to part (a).
(8)
ома
(1)
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