p^i is the four-momentum and u_i is the four-velocity, why p^i u_i = (mc)^2

Helpful information: (1) An alpha particle is a helium nucleus, (2) e = 1.6 × 10-¹⁹ C, (3) k = 9.0 × 10⁹ Nm² C-2, (4) 1nm = 1 × 10-⁹ m 1-An alpha particle lies on the x-axis, a distance of 1.0 nanometer from a proton (in this set-up, the alpha particle is at the origin while the proton is in the positive direction). Which of the following choices below represents the magnitude of the electric force on the alpha particle? (a) 2.3 × 10-10 N (b) 4.6 × 10-¹0 N (c) 2.3 × 10-19 N (d) 4.6 × 10-19 N eplacing the voltage sou the following inst choices below time != 1.00 37 instantaneous current

Two protons collide and form a neutral pion through this interaction: Proton + proton --> proton + proton + pion. Protons have a mass of 938 MeV/c2 and the pion 135 MeV/c2. In the scenario where both incident protons are moving with the same speed, in opposite directions, what is the minimum kinetic energy for the protons to have to be able to produce the neutral pion as described above? Thanks

a) A K° meson (mass 497.61 MeV/c2) decays to a t, T pair with a mean lifetime of 0.89 x 10-10 s. Suppose the K° has a kinetic energy of 276 MeV when it decays, and that the two A mesons emerge at equal angles to the original K° direction. Calculate the kinetic energy of each T meson and the opening angle between them. The mass of a 7 meson is 139.57 MeV/c2.

What is the wavelength, in fm (femtometers, or 10^-15 m), of a proton travelling at 90% of the speed of light?

A galaxy G is moving away radially with speed with respect to an observer O. The relation between X, the wavelength of light emitted at G, and λo, the wavelength observed at O, is 入。 λ = λe λε 1+B 1- B' = where ẞ v/c (c is the speed of light). For ẞ < 1 find a power series expansion of the above formula up to and including terms of order ẞ³.