QCAA Physics Alternative Sequence Special relativity

Because Observer 2 measures the train to be shorter than the tunnel, the train will fully enter the tunnel before its front exits, meaning these events are not simultaneous.

The train's mass is an invariant property (rest mass) or depends only on its speed (relativistic mass), neither of which changes simply by entering the tunnel.

The train is traveling at a constant relativistic speed; entering the tunnel does not exert a force to cause it to accelerate.

Observer 1 measures the train's proper length as 95 m and the tunnel's contracted length as 95 m. Therefore, Observer 2 measures the tunnel's proper length ($> 95$ m) and the train's contracted length ($< 95$ m), making the train shorter than the tunnel.

Correct. This is Einstein's famous mass-energy equivalence formula, stating that energy ($E$) equals mass ($m$) times the speed of light squared ($c^2$).

Incorrect. This is the formula for gravitational potential energy, where $g$ is the acceleration due to gravity and $h$ is height.

Incorrect. This incorrectly combines the structure of the kinetic energy formula with the speed of light ($c$), which does not represent any standard physical relationship.

Incorrect. This is the classical formula for kinetic energy, representing the energy of an object in motion with mass $m$ and velocity $v$.