A mass of M kg suspended by a weightless string and a horizontal force that is applied to displace the mass until the string makes an angle of 45 with the initial vertical direction. Find the force

Here, the constant horizontal force required to take the body from position 1 to position 2 can be calculated by using work energy theorem. Let us assume that body taken slowly so that its speed doesn't change, then ΔK = 0=WF+WMg+Wtension (symbols have their usual meanings)WF=F×lsin⁡45∘,WMg= -Mgl−lcos45∘,Wtension =0∴F=Mg(2−1)