In his first e/m experiment Thomson determined the speed of electrons accelerated through a potential V by

In his first e/m experiment Thomson determined the speed of electrons accelerated through a potential ΔV by collecting them in an insulated beam stopper and measuring both the total collected charge Q and the temperature rise ΔT of the beam stopper.
(a) Show that with those measurements, he could obtain an expression for e/m in terms of the speed of the electrons and the directly measured quantities. 

(b) Show that the expression obtained in (a) together with the result of Problem 3-2 enabled Thomson to compute e/m in terms of directly measured quantities.