An investigator wants to identify a mysterious substance found at a crime scene.

Question

An investigator wants to identify a mysterious substance found at a crime scene. To
do this the investigator uses a mass spectrometer. Inside the spectrometer the substance is
bombarded with electrons to create charged molecules (ions). These ions are then exposed
to an electric field to accelerate them toward a detector. The spectrometer measures the
flight time to determine how massive the ions are.
The mystery substance is composed of two molecules A and B with mass mA = 150 atomic
units and mB = 375 atomic units (1 amu = 1.66

Explanation / Answer

F = qE

a = qE/m

in this case, q = -e, -2e for A and B.

m = mA, mB

a = -eE/mA, -2eE/mA, -eE/mB, -2eE/mB

e = 1.602x10-19 C,

mA = 150x1.66x10-27 kg,

mB = 375x1.66x10-27 kg

E = 6500 V/m

aA = 41.8193x108 m/s2

aA2 = 83.6386x108 m/s2

aB = 16.7277x108 m/s2

aB2 = 33.4554x108 m/s2

Obviously, A2- reaches first since it has max acceleration

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