A knight on horseback holds a 10-m lance.The horse can run at 0.70 c.(It wins most of its races!)How long will the lance appear to a person that is standing still on the ground as the horse runs past?
A)7.1 m
B)10 m
C)14 m
D)15 m

Question

Quizplus · Accepted Answer

Due to the effects of special relativity, specifically length contraction, the lance will appear shorter to a stationary observer. The contracted length L is given by L = L0 * sqrt(1 - v^2/c^2), where L0 is the proper length (10 m), v is the velocity (0.70c), and c is the speed of light. Calculating this gives approximately 7.1 m.

A Knight on Horseback Holds a 10-M Lance