Reading Passage Problems
BI O Heartbeat detector A prisoner tries to escape from a Nashville, Tennessee prison by hiding in the laundry truck. The prisoner is surprised when the truck is stopped at the gate. A guard enters the truck and handcuffs him. “How did you know I was here?” the prisoner asks. “The heartbeat detector,” says the guard. A heartbeat detector senses the tiny vibrations caused by blood pumped from the heart. With each heartbeat, blood is pumped upward to the aorta, and the body recoils slightly, conserving the momentum of the blood-body system. The body’s vibrations are transferred to the inside of the truck. Vibration sensors on the outside of the truck are linked to a geophone, or signal amplifier, attached to a computer. A wave analyzer program in the computer compares vibration signals from the truck to wavelets produced by heartbeat vibrations. The wave analyzer distinguishes a person’s heartbeat from other vibrations in the truck or in the surrounding environment, allowing guards to detect the presence of a human in the truck.
What can be used to analyze the motion of a person’s body hidden inside a car or truck (choosing the body and blood as a system)?
(a) The idea that mass of an isolated system is constant
(b) The idea that momentum of an isolated system is constant
(c) The impulse-momentum principle
(d) a and b
(e) b and c
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