A particle of mass m moving with a velocity u makes an elastic one dimensional collision with a stationary particle of mass m establishing a contact with it for extremely small time T. Their force of contact increases from zero to F₀ linearly in time $\frac{\mathrm{T}}{4}$, remains constant for a further time $\frac{\mathrm{T}}{2}$ and decreases linearly from F₀ to zero in further time $\frac{\mathrm{T}}{4}$ as shown. The magnitude possessed by F₀ is