Paper 3 · Work, Energy and Power
Starting from W = Fx, with F = ma and v^2 = u^2 + 2ax for a body accelerated from rest (u = 0), what equation for kinetic energy Ek does this derivation give, in terms of mass m and speed v?
Model answer
0.5mv^2
Also accepted: Ek = 1/2 mv^2, mv^2/2
Explanation: With u=0, v^2=2ax so x=v^2/(2a). Substituting F=ma into W=Fx gives W = ma*v^2/(2a) = (1/2)mv^2, which is the kinetic energy gained.
Derived from ZIMSEC Physics Paper 3, November 2004, Q1