Chapter 6, Problem 80RPP

BIO 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.

A heartbeat detector relies on a geophone placed against the exterior of a truck or car. What can cause the vibrations of the truck or car?

a. Wind

b. Ground vibrations due to other moving cars or trucks

c. Vibrations of passengers in the car or truck

d. All of the above