A thin, uniform bar of length L and mass M is suspendedhorizontally at rest. It is suddenly released
and, at the same instant, it is struck a sharp blow verticallyupwards at one end – the duration of
the impulse is negligibly short.
(a) Explain the meaning of the equation Fnet = Macom (com standsfor center of mass). If we call z the vertical direction, write anequation for zCOM(t), draw a sketch of zCOM(t) vs t, and annotateit to show the initial
slope, the maximum value of zCOM(t), and the time(s) at whichzCOM(t) = 0.
(b) Explain the meaning of the equation Tnet = Iα (net torque).Describe the rotational motion of the bar, by
giving an equation for the angular displacement θ(t). (Themoment of inertia of a bar about
a perpendicular axis through its centre is 1/12ML^2.)
(c) By combining your answers to (a) and (b), describe in wordshow the bar moves after being
struck. (Note: you can try the experiment yourself, using a penas the bar, and your ï¬nger
or another pen to impart the impulse.)
