The secondary unbalanced force due to inertia of reciprocating parts in a reciprocating engine is given by (where m = Mass of reciprocating parts, ω = Angular speed of crank, r = Radius of crank, θ = Angle of inclination of crank with the line of stroke, and n = Ratio of the length of connecting rod to radius of crank)

• A. m.ω².r sinθ
• B. m.ω².r (sin 2θ/n)
• C. m.ω².r cosθ
• D. m.ω².r (cos 2θ/n)

Answer: (D)