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SAT® Subject Test in Physics

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Difficult

Particles Flying in the Sky

SATPHY-QYFCG1

A scientist standing on the earth detects a stream of radioactive particles (with very short half-lives) flying through the atmosphere with velocities close to the speed of light. The scientist is able to measure the mass of the particles, the average time they take to decay, and the distance they travel (all the same), while in flight.

We'll call the mass he measures in flight $M$ the average decay time $T$ and the distance they travel $D$

The scientist measures the same three quantities for originally undecayed particles while they are at rest. He measures the same path they took through the atmosphere to get the distance traveled. He comes up with $m$ for the mass of the particles, $t$ for the average decay time, and "d" for the distance they travelled.

Which table accurately describes the relationship between the measured quantities for the particles while in flight and then while at rest?

A
particle mass M < m
average decay time T > t
distance traveled D < d
B
particle mass M > m
average decay time T < t
distance traveled D = d
C
particle mass M < m
average decay time T < t
distance traveled D < d
D
particle mass M = m
average decay time T < t
distance travelled D = d
E
particle mass M > m
average decay time T > t
distance travelled D = d