Question 1

Paper 2Medium4 marks

In inertial frame SS a particle moves along the xx-axis as shown in Figure 1. Inertial frame S′S' moves in the +x+x-direction at speed v=0.50cv=0.50c relative to SS The origins of the frames coincide at t=t′=0t=t'=0 Take c=3.00×108 m s−1c=3.00\times10^8\ \mathrm{m\,s^{-1}}

The Lorentz transformations are

x′=γ(x−vt),t′=γ(t−vxc2),γ=11−v2/c2.x'=\gamma(x-vt),\qquad t'=\gamma\left(t-\frac{vx}{c^2}\right), \qquad \gamma=\frac{1}{\sqrt{1-v^2/c^2}}.
01234500.10.20.30.40.50.60.70.80.91t / nsx / m
(a)

Determine u/cu/c for the particle in frame SS

[1]
(b)

For two events on the particle’s motion, use the Lorentz transformations to show that

u′=u−v1−uv/c2.u'=\frac{u-v}{1-uv/c^2}.
[2]
(c)

Use your answers to (a) and (b) to determine u′/cu'/c to 2 significant figures.

[1]

More A.5 Galilean and special relativity questions