Plot[1-((Cos[2.5 π t]+q Cos[5 π t])/(1+q))/.q->1,{t,0,.8},Frame->True,FrameLabel->{a,a},LabelStyle->Directive[FontSize->14]]

Manipulate[Plot[1-((Cos[2.5 π t]+q Cos[5 π t])/(1+q)),{t,0,0.8},PlotRange->{{0,.8},{0,2}},Frame->True,FrameLabel->{"Time","Force"},LabelStyle->Directive[FontSize->14]],{q,0,2}]