In research in cardiology and exercise physiology, it is often important to know the mass of blood pumped by a person’s heart in one stroke. This information can be obtained by means of a ballistocardiograph . The instrument works as follows. The subject lies on a horizontal pallet floating on a film of air. Friction on the pallet is negligible. Initially, the momentum of the system is zero. When the heart beats, it expels a mass m of blood into the aorta with speed υ, and the body and platform move in the opposite direction with speed V The blood velocity can be determined independently (e.g., by observing the Doppler shift of ultrasound). Assume that it is 50.0 cm/s in one typical trial. The mass of the subject plus the pallet is 54.0 kg. The pallet moves 6.00 × 10 -5 m in 0.160 s after one heartbeat. Calculate the mass of blood that leaves the heart. Assume that the mass of blood is negligible compared with the total mass of the person. (This simplified example illustrates the principle of ballistocardiography, but in practice a more sophisticated model of heart function is used.)
In research in cardiology and exercise physiology, it is often important to know the mass of blood pumped by a person’s heart in one stroke. This information can be obtained by means of a ballistocardiograph . The instrument works as follows. The subject lies on a horizontal pallet floating on a film of air. Friction on the pallet is negligible. Initially, the momentum of the system is zero. When the heart beats, it expels a mass m of blood into the aorta with speed υ, and the body and platform move in the opposite direction with speed V The blood velocity can be determined independently (e.g., by observing the Doppler shift of ultrasound). Assume that it is 50.0 cm/s in one typical trial. The mass of the subject plus the pallet is 54.0 kg. The pallet moves 6.00 × 10 -5 m in 0.160 s after one heartbeat. Calculate the mass of blood that leaves the heart. Assume that the mass of blood is negligible compared with the total mass of the person. (This simplified example illustrates the principle of ballistocardiography, but in practice a more sophisticated model of heart function is used.)
Solution Summary: The author calculates the mass of blood that leaves the heart by calculating the velocity of the pallet.
In research in cardiology and exercise physiology, it is often important to know the mass of blood pumped by a person’s heart in one stroke. This information can be obtained by means of a ballistocardiograph. The instrument works as follows. The subject lies on a horizontal pallet floating on a film of air. Friction on the pallet is negligible. Initially, the momentum of the system is zero. When the heart beats, it expels a mass m of blood into the aorta with speed υ, and the body and platform move in the opposite direction with speed V The blood velocity can be determined independently (e.g., by observing the Doppler shift of ultrasound). Assume that it is 50.0 cm/s in one typical trial. The mass of the subject plus the pallet is 54.0 kg. The pallet moves 6.00 × 10-5 m in 0.160 s after one heartbeat. Calculate the mass of blood that leaves the heart. Assume that the mass of blood is negligible compared with the total mass of the person. (This simplified example illustrates the principle of ballistocardiography, but in practice a more sophisticated model of heart function is used.)
PROBLEM 2
A cube of mass m is placed in a rotating funnel.
(The funnel is rotating around the vertical axis shown
in the diagram.) There is no friction between the cube
and the funnel but the funnel is rotating at just the
right speed needed to keep the cube rotating with the
funnel. The cube travels in a circular path of radius r,
and the angle between the vertical and the wall of the
funnel is 0. Express your answers to parts (b) and (c)
in terms of m, r, g, and/or 0.
(a) Sketch a free-body diagram for the cube. Show
all the forces acting on it, and show the appropriate
coordinate system to use for this problem.
(b) What is the normal force acting on the cube?
FN=mg58
(c) What is the speed v of the cube?
(d) If the speed of the cube is different from what you
determined in part (c), a force of friction is necessary
to keep the cube from slipping in the funnel. If the
funnel is rotating slower than it was above, draw a
new free-body diagram for the cube to show which
way friction…
Circular turns of radius r in a race track are often banked at an angle θ to allow the cars to achieve higher speeds around the turns. Assume friction is not present.
Write an expression for the tan(θ) of a car going around the banked turn in terms of the car's speed v, the radius of the turn r, and g so that the car will not move up or down the incline of the turn.
tan(θ) =
The character Min Min from Arms was a DLC character added to Super Smash Bros. Min Min’s arms are large springs, with a spring constant of 8.53 ⋅ 10^3 N/m, which she uses to punch and fling away her opponents. Min Min pushes her spring arm against Steve, who is not moving, compressing it 1.20 m as shown in figure A. Steve has a mass of 81.6 kg. Assuming she uses only the spring to launch Steve, how fast is Steve moving when the spring is no longer compressed? As Steve goes flying away he goes over the edge of the level, as shown in figure C. What is the magnitude of Steve’s velocity when he is 2.00 m below where he started?
Chapter 9 Solutions
Physics for Scientists and Engineers, Technology Update (No access codes included)
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